1904 (MCMIV) was a leap year starting on Friday (dominical letter CB) of the Gregorian calendar and a leap year starting on Thursday (dominical letter DC) of the Julian calendar, the 1904th year of the Common Era (CE) and Anno Domini (AD) designations, the 904th year of the 2nd millennium, the fourth year of the 20th century, and the fifth year of the 1900s decade. As of the start of 1904, the Gregorian calendar was 13 days ahead of the Julian calendar, which remained in localised use until 1918.
- January 7 – The distress signal CQD is established, only to be replaced 2 years later by SOS.
- January 12 – Henry Ford sets a new automobile land speed record of 91.37 mph (147.05 km/h).
- January 16 – The first large-scale bodybuilding competition in America takes place at Madison Square Garden in New York City.
- January 18 – The Herero Rebellion in German South-West Africa begins.
- January 23 – The Ålesund Fire destroys most buildings in the town of Ålesund, Norway, leaving about 10,000 people without shelter.
- January 25 – Halford Mackinder presents a paper on "The Geographical Pivot of History" to the Royal Geographical Society of London in which he formulates the Heartland Theory, originating the study of geopolitics.
- February 7 – The Great Baltimore Fire in Baltimore, Maryland, destroys over 1,500 buildings in 30 hours.
- February 8–9 – Battle of Port Arthur: A surprise Japanese naval attack on Port Arthur (Lüshun) in Manchuria starts the Russo-Japanese War.
- February 10 – Roger Casement publishes his account of Belgian atrocities in the Congo.
- February 17 – Puccini's opera Madama Butterfly, with a background theme of Japan–United States relations, debuts at La Scala in Milan to no great acclaim. On May 28 a revised version opens in Brescia to huge success.
- February 23 – For $10 million, the United States gains control of the Panama Canal Zone.
- February 28 – Sport Lisboa e Benfica is founded in Portugal.
- March 3 – Kaiser Wilhelm II of Germany becomes the first person to make a political recording of a document, using Thomas Edison's cylinder.
- March 4 – Russo-Japanese War: Russian troops in Korea retreat toward Manchuria, followed by 100,000 Japanese troops.
- March 26 – 80,000 demonstrators gather in Hyde Park, London, to protest against the importation of Chinese labourers to South Africa by the British government.
- March 31 – British expedition to Tibet – Battle of Guru: British troops under Colonel Francis Younghusband defeat ill-equipped Tibetan troops.
- April 6 – Joseph F. Smith announces the Second Manifesto in General Conference of The Church of Jesus Christ of Latter-day Saints, ending in fact the practise of plural marriage which had continued to be practised by a large number of of its leaders in violation of the 1890 Manifesto officially banning the practice.
- April 8
- April 19 – The Great Toronto Fire destroys much of that city's downtown, but there are no fatalities.
- April 27 – The Australian Labor Party becomes the first such party to gain national government, under Chris Watson.
- April 30 – The Louisiana Purchase Exposition World's Fair opens in St. Louis, Missouri (closes December 1).
- May 4
- May 5
- Pitching against the Philadelphia Athletics, Cy Young of the Boston Americans throws the first perfect game in the modern era of baseball.
- British expedition to Tibet: Hundreds of Tibetans attack the British camp at Changlo and, for a while, hold the advantage before being defeated by superior weapons and losing at least 200 men.
- May 9 – Great Western Railway of England 3700 Class 3440 City of Truro becomes the first railway locomotive to exceed 100 mph (probably).
- May 15– The Russian minelayer Amur lays a minefield about 15 miles (24 km) off Port Arthur and sinks Japan's battleships Hatsuse, 15,000 tons, with 496 crew and Yashima.
- May 21 – The International Federation of Association Football, FIFA, is established.
- May 30 – Alpha Gamma Delta, which becomes an international women's fraternity, is founded by 11 women at Syracuse University.
- June 10 – Irish author James Joyce meets his future wife Nora Barnacle.
- June 15 – A fire aboard the steamboat General Slocum in New York City's East River kills 1,021.
- June 16
- June 28 – The Danish ocean liner SS Norge runs aground and sinks close to Rockall, killing 635, including 225 Norwegian emigrants.
- June 28 – The original icon of Our Lady of Kazan was stolen and subsequently destroyed in Russia.
- June 29 – The 1904 Moscow tornado occurs.
- July 1 – The third Modern Olympic Games opens in St. Louis, Missouri, United States as part of the World's Fair is first Summer Olympic Games of the 20th Century.
- August 3 – British expedition to Tibet: The British expedition under Colonel Francis Younghusband takes Lhasa in Tibet.
- August 11 – Battle of Waterberg: Lothar von Trotha defeats the Herero in German South-West Africa and drives them into the Omaheke desert, start of the Herero and Namaqua Genocide.
- August 14 – Ismael Montes becomes President of Bolivia.
- August 17 – Russo-Japanese War: A Japanese infantry charge fails to take Port Arthur.
- August 18 – Chris Watson resigns as Prime Minister of Australia and is succeeded by George Reid.
- August 22 – China's Deng Xiaoping (邓小平）is born in Sichuan Province.
- September 7 – British expedition to Tibet: The Dalai Lama signs the Anglo-Tibetan Treaty with Colonel Francis Younghusband.
- September 25 – The Church of Jesus Christ of Latter-day Saints President Joseph F. Smith issues a Second Manifesto against polygamy.
- September 26 – New Zealand dolphin Pelorus Jack is individually protected by Order in Council under the Sea Fisheries Act.
- October 1 – Phi Delta Epsilon, the international medical fraternity, is founded by Aaron Brown and eight of his friends at Cornell University Medical College.
- October 5 – Alpha Kappa Psi, the co-ed Professional Business Fraternity, is founded on the campus of New York University.
- October 9 – German journalist Anna Rüling, in a speech to the Scientific-Humanitarian Committee in Berlin, makes the first known public statement of the socio-legal problems faced by lesbians.
- October 15 – Theta Tau, the Professional Engineering Fraternity, is founded at the University of Minnesota in Minneapolis.
- October 19 – Polytechnic University of the Philippines is founded as Manila Business School through the superintendence of the American C.A. O'Reilley.
- October 21 – Russo-Japanese War – Dogger Bank incident: The Russian Baltic Fleet fires on British trawlers it mistakes for Japanese torpedo boats in the North Sea.
- October 27 – The first underground line of the New York City Subway opens.
- October 28 – Panama and Uruguay establishes diplomatic links.
- November 8 – U.S. presidential election, 1904: Republican incumbent Theodore Roosevelt defeats Democrat Alton B. Parker.
- November 16 – The settlement at Grytviken on the British South Atlantic island territory of South Georgia is established by Norwegian sea captain Carl Anton Larsen as a whaling station for his Compañía Argentina de Pesca.
- November 24 – The first successful caterpillar track is made (it later revolutionises construction vehicles and land warfare).
- December 2 – The St. Petersburg Soviet urges a run on the banks: the attempt fails and the executive committee is arrested.
- December 3 – Charles Dillon Perrine discovers Jupiter's largest irregular satellite, Himalia.
- December 4 – The K.U. or Konservativ Ungdom (Young Conservatives) is founded by Carl F. Herman von Rosen in Denmark.
- December 6 – Theodore Roosevelt announced his "Corollary" to the Monroe Doctrine, stating that the United States would intervene in the Western Hemisphere should Latin American governments prove incapable or unstable.
- December 10 – The Pi Kappa Phi fraternity is founded at the College of Charleston in Charleston, SC.
- December 27 – The stage play Peter Pan, or The Boy Who Wouldn't Grow Up premieres in London.
- December 30 – The East Boston Tunnel opens.
- December 31 – In New York City, the first New Year's Eve celebration is held in Times Square.
- The Loftus Road and Griffin Park football stadiums open in London.
- Stuyvesant High School is founded in New York City.
- St. Bernard's School is founded in New York City.
- The Daytona Educational and Industrial Training School for Negro Girls, now Bethune-Cookman University, is founded.
- The subject of alcohol and heart attacks is first investigated.
- January 1 – Fazal Ilahi Chaudhry, Pakistani politician (d. 1982)
- January 5 – Jeane Dixon, American astrologer (d. 1997)
- January 10 – Ray Bolger, American actor, singer, and dancer (The Wizard of Oz)(d. 1987)
- January 13 – Richard Addinsell, British composer (d. 1977)
- January 14
- January 18 – Cary Grant, English actor (d. 1986)
M.D.one of the pioneers in medical research who helped to prove the worth of the oral contraceptive pill
- January 21 – Edris Rice-Wray Carson (d. 1990)
- January 22
- January 26
- January 27 – J. J. Gibson, American psychologist (d. 1979)
- January 28 – Canuplin, Filipino magician and bodabil entertainer (d. 1979)
- January 29 – Arnold Gehlen, German philosopher (d. 1976)
- February 1
- February 3
- February 4 – MacKinlay Kantor, American writer and historian (d. 1977)
- February 10
- February 11 – Sir Keith Holyoake, Prime Minister of New Zealand (d. 1983)
- February 16
- February 20 – Alexei Kosygin, Premier of the Soviet Union (d. 1980)
- February 22 – Ernst Jakob Henne, German motorcycle racer and racecar driver (d. 2005)
- February 29 – Jimmy Dorsey, American bandleader (d. 1957)
- March 1
- March 2 – Dr. Seuss, American children's author (The Cat in the Hat) (d. 1991)
- March 4
- March 5 – Mow Pang Tzu, Republic of China air force general (d. 1987)
- March 6 – Hugh Williams, English actor and dramatist (d. 1969)
- March 7 – Reinhard Heydrich, German Nazi official (d. 1942)
- March 14 – Doris Eaton Travis, American actress (d. 2010)
- March 15 – J. Pat O'Malley, English actor (d. 1985)
- March 20 – Frank Mills (politician), American politician in Ohio legislature (1969)
- March 22 – Itche Goldberg, Yiddish author (d. 2006)
- March 26
- April 1 – Nikolai Berzarin, Russian Red Army General (d. 1945)
- April 3 – Sally Rand, American dancer and actress (d. 1979)
- April 6 – Kurt Georg Kiesinger, former Chancellor of West Germany (d. 1988)
- April 8 – John Hicks, English economist, Nobel Prize laureate (d. 1989)
- April 9 – Sharkey Bonano, American jazz musician (d. 1972)
- April 13 – Elwood "Pete" Quesada, American air force general (d. 1993)
- April 14 – John Gielgud, English actor (d. 2000)
- April 15 – Arshile Gorky, Armenian-born painter (d. 1948)
- April 16 – Fifi D'Orsay, Canadian actress (d. 1983)
- April 22 – J. Robert Oppenheimer, American physicist (d. 1967)
- April 24 – Willem de Kooning, Dutch artist (d. 1997)
- April 26 – Jimmy McGrory, Scottish footballer (d. 1982)
- April 27 – Cecil Day-Lewis, English poet (d. 1972)
- April 29 – Pedro Vargas, Mexican singer and actor (d. 1989)
- May 4
- May 6
- May 8 – John Snagge, British radio personality (d. 1996)
- May 10 – James Roy Andersen, American general (d. 1945)
- May 11 – Salvador Dalí, Spanish artist (d. 1989)
- May 17
- May 20 – Margery Allingham, British detective fiction writer (d. 1966)
- May 21
- May 22 – Anne de Vries, Dutch writer (d. 1964)
- May 25 – Charles L. Melson, United States Navy admiral (d. 1981)
- May 26 – George Formby, English singer and comedian (d. 1961)
- May 27 – Chūhei Nambu, Japanese athlete (d. 1997)
- May 30 – Doris Packer, American actress (d. 1979)
- June 2
- June 3 – Jan Peerce, American tenor (d. 1984)
- June 6
- June 18 – Keye Luke, American actor (d. 1991)
- June 22 – William O. Gallery, American admiral (d. 1981)
- June 24 – Phil Harris, American actor (d. 1995)
- June 26 – Peter Lorre, Hungarian-born film actor (d. 1964)
- July 2 – René Lacoste, French tennis player and businessman (d. 1996)
- July 5 – Ernst Mayr, German-born biologist and author (d. 2005)
- July 6 – Erik Wickberg, General of The Salvation Army (d. 1996)
- July 8 – Henri Cartan, French mathematician (d. 2008)
- July 12 – Pablo Neruda, Chilean poet, Nobel Prize laureate (d. 1973)
- July 15 – Rudolf Arnheim, German-born author (d. 2007)
- July 24 – Nikolay Gerasimovich Kuznetsov, Soviet admiral (d. 1974)
- July 26 – Edwin Albert Link, American pioneer in aviation, underwater archaeology, submersibles, inventor of aeronautical, navigation, and oceanographic equipment (d. 1981)
- July 28 – Pavel Cherenkov, Soviet physicist, Nobel Prize laureate (d. 1990)
- July 29 – J. R. D. Tata, Indian businessman (d. 1993)
- August 4
- August 7 – Ralph Bunche, American diplomat, recipient of the Nobel Peace Prize (d. 1971)
- August 12 – Alexei Nikolaevich, Tsarevich of Russia (d. 1918)
- August 13
- August 16
- August 17
- August 19 – George de la Warr, British alternative physician (d. 1969)
- August 21 – Count Basie, American musician and bandleader (d. 1984)
- August 22
- August 23
- August 24 – Ida Cook, English campaigner for Jewish refugees, and romantic novelist as Mary Burchell (d. 1986)
- August 26 – Christopher Isherwood, English writer (d. 1986)
- August 28 – Secondo Campini, Italian jet pioneer (d. 1980)
- August 29 – Werner Forssmann, German physician, recipient of the Nobel Prize in Physiology or Medicine (d. 1979)
- September 9 – Feroze Khan, Pakistani field hockey player (d. 2005)
- September 12 – Lou Moore, American race car driver and team owner (d. 1956)
- September 14 – Richard Mohaupt, German composer and Kapellmeister (d. 1957)
- September 19 – Elvia Allman, American actress (d. 1992)
- September 29 – Greer Garson, English actress (d. 1996)
- October 1
- October 3 – Charles J. Pedersen, American chemist, Nobel Prize laureate (d. 1989)
- October 9 – Wally Brown, American actor and comedian (d. 1961)
- October 18 – Haim Shirman, Russian-born Israeli professor of mediaeval Spanish Jewish poetry (d. 1981)
- October 20 – Tommy Douglas, Canadian politician (d. 1986)
- October 23 – Harvey Penick, American golfer (d. 1995)
- October 25 – Vladimir Peter Tytla, American animator (d. 1968)
- November 1 – Laura La Plante, American silent film actress (d. 1996)
- November 2 – Hugh Lygon, English aristocrat (d. 1936)
- November 4 – Tadeusz Żyliński, Polish technician and textilist (d. 1967)
- November 11
- November 12 – Jacques Tourneur, French director (d. 1977)
- November 14
- November 16 – Nnamdi Azikiwe, President of Nigeria (d. 1996)
- November 18 – Masao Koga, Japanese composer (d. 1978)
- November 22 – Louis Néel, French physicist, Nobel Prize laureate (d. 2000)
- November 25
- November 30 – Clyfford Still, American painter (d. 1980)
- December 4 – Albert Norden, German politician (d. 1982)
- December 6 – Ève Curie, French author (d. 2007)
- December 7 – Clarence Nash, American voice actor (d. 1985)
- December 12 – Baron Nicolas de Gunzburg, French-born magazine editor and socialite (d. 1981)
- December 18 – George Stevens, American film director (d. 1975)
- December 20 – Rambai Barni Svastivatana, Queen consort of King Prajadhipok of Siam. (d. 1984)
- December 24
- December 25
- December 26 – Alejo Carpentier, Cuban writer (d. 1980)
- December 30
- Bernard Castro, Italian inventor (d. 1991)
- Tevfik Esenç, Turkish-born last speaker of the Ubykh language (d. 1992)
- Soeman Hs, Indonesian author and educator (d. 1999)
- January 2 – James Longstreet, Confederate Civil War general (b. 1821)
- January 7 – Emmanuel Rhoides, Greek writer (b. 1836)
- January 10 – Jean-Léon Gérôme, French painter (b. 1824)
- January 17 – Sir Henry Keppel, British admiral (b. 1809)
- February 4 – Rudolf Maison, German sculptor (b. 1854)
- February 8 – Alfred Ainger, English biographer (b. 1837)
- February 15 – Mark Hanna, United States Senator from Ohio (b. 1837)
- February 22 – Leslie Stephen, English writer and critic (b. 1832)
- March 5
- March 17 – Prince George, Duke of Cambridge, grandson of King George III (b. 1819)
- March 18 – William Elbridge Sewell, American naval officer and Governor of Guam (b. 1851)
- April 5 – Tom Allen, British boxing champion (b. 1840)
- April 10 – Queen Isabella II of Spain (b. 1830)
- April 13 – Stepan Makarov, Russian admiral (killed in action) (b. 1849)
- May 1 – Antonín Dvořák, Czech composer (b. 1841)
- May 6 – Franz von Lenbach, German painter (b. 1836)
- May 7 – Manuel Candamo, Peruvian politician, thirtieth President of Peru (b. 1841)
- May 8 – Eadweard Muybridge, English photographer and motion picture pioneer (b. 1830)
- May 10 – Henry Morton Stanley, Welsh explorer and journalist (b. 1841)
- May 19 – Auguste Molinier, French historian (b. 1851)
- June 3 – Vincent Tancred, South African cricketer (b. 1875)
- June 4 – George Frederick Phillips, Canadian-born military hero (b. 1862)
- June 12 – Camille of Renesse-Breidbach, Belgian Count (b. 1836)
- June 16 – Nikolay Bobrikov, Russian soldier and politician, Governor-General of Finland (b. 1839)
- June 22 – Karl Ritter von Stremayr, former Prime Minister of Austria (b. 1832)
- July 1 – George Frederic Watts, British symbolist painter and sculptor (b. 1817)
- July 3 – Theodor Herzl, Austrian founder of Zionism (b. 1860)
- July 6 – Abai Qunanbaiuli, Kazakh poet (b. 1845)
- July 14 – Paul Kruger, President of the South African Republic. (b. 1825)
- July 15 – Anton Chekhov, Russian writer (b. 1860)
- July 26 – Henry Clay Taylor, American admiral (b. 1845)
- August 6 – Eduard Hanslick, Austrian music critic (b. 1825)
- August 10
- August 12
- August 16 – Colonel Prentiss Ingraham, American author of dime fiction (b. 1843)
- August 22 – Kate Chopin, American author (b. 1850)
- August 25 – Henri Fantin-Latour, French painter (b. 1836)
- August 29 – Ottoman Sultan Murad V (b. 1840)
- September 22 – Wilson Barrett, English actor (b. 1846)
- September 24 – Niels Ryberg Finsen, Icelandic/Faroese/Danish physician and scientist (b. 1860)
- September 26
- October 4
- October 15 – George, King of Saxony (b. 1832)
- October 21 – Isabelle Eberhardt, Swiss-Algerian explorer (b. 1877)
- November 28 – Fanny Janauschek, Czech actress (b. 1829)