The year 1903 in science and technology involved some significant events, listed below.

• June 27–19-year-old American socialite Aida de Acosta becomes the first woman to fly a powered aircraft solo when she pilots Santos-Dumont's motorized dirigible, "No. 9", from Paris to Château de Bagatelle in France.^[1]
• December 17 – First documented, successful, controlled, powered flight of a heavier-than-air aircraft with a petrol engine by Orville Wright in the Wright Flyer at Kill Devil Hills, North Carolina.
• Konstantin Tsiolkovsky begins a series of papers discussing the use of liquid fuel rockets to reach outer space, space suits, and colonization of the Solar System.

• The type specimen of the vampire squid (Vampyroteuthis infernalis) is described by Carl Chun.^[2]
• Fauna and Flora International is founded as the Society for the Preservation of the Wild Fauna of the Empire by a group of British naturalists and American statesmen in Africa.

• Peter Cooper Hewitt demonstrates the mercury-vapour lamp.
• Mikhail Semyonovich Tsvet invents chromatography, an important analytic technique.
• The International Committee of Atomic Weights publishes the inaugural atomic weights report.

• October – Frank Nelson Cole demonstrates that the Mersenne number 2⁶⁷-1, or M₆₇, is composite by factoring it as 193,707,721 * 761,838,257,287.^[3]
• Fast Fourier transform algorithm presented by Carle David Tolmé Runge.^{[citation needed]}
• Edmund Georg Hermann Landau gives considerably simpler proof of the prime number theorem.

• George Darwin and John Joly claim that radioactivity is partially responsible for the Earth's heat.
• Prosper-René Blondlot claims to have detected N rays.

• March–April – David Bruce identifies the parasitic Trypanosoma protist as the source of African trypanosomiasis ("sleeping sickness").^[4]
• May 10 – Antoni Leśniowski publishes the first article implicating what will later be known as Crohn's disease, in the Polish weekly medical newspaper Medycyna.^[5]
• Alfred Walter Campbell divides the cytoarchitecture of the human brain into 14 areas.^[6]
• Ernest Fourneau synthesizes and patents Amylocaine, the first synthetic local anesthetic, under the name Stovaine at the Pasteur Institute.^[7]
• Willem Einthoven discovers electrocardiography (ECG/EKG)
• Percy Furnivall carries out the first known case of cardiac surgery in Britain.
• The 12th and final edition of Dr Richard von Krafft-Ebing's Psychopathia Sexualis: eine Klinisch-Forensische Studie ("Sexual Psychopathy: a Clinical-Forensic Study") published during the author's lifetime introduces the term paedophilia erotica.
• Formal opening of the Johnston Laboratories at the University of Liverpool, Liverpool, England.

• November – Windscreen wiper for automobiles is first patented by Mary Anderson in the United States.
• December 15 – Italo Marchiony from New York City patents an improved design of apparatus for baking ice cream cones.^[8]
• The first diesel-powered ships are launched, both for inland waters: Petite-Pierre in France, powered by Dyckhoff-built diesels, and the tanker Vandal in Russia, powered by Swedish-built diesels with an electrical transmission.
• Norwegian engineer Ægidius Elling builds the first gas turbine to generate power, using a centrifugal compressor.^[9]
• Laminated glass is invented by Edouard Benedictus.
• Baker valve gear for steam locomotives is first patented in the United States.^[10]
• The Lune Valley boiler is patented by John G. A. Kitchen and Ludlow Perkins.^[11]

• June 28 – Deutsches Museum founded in Munich.^[12]

• Nobel Prizes
  • Physics – Antoine Henri Becquerel, Pierre Curie, and Marie Curie^[13]
  • Chemistry – Svante August Arrhenius
  • Medicine – Niels Ryberg Finsen

• January 22 – Fritz Houtermans (died 1966), Danzig-born Dutch physicist.
• January 27 – John Eccles (died 1997), Australian-born psychologist.
• January 28 – Kathleen Lonsdale, née Yardley (died 1971), Irish-born crystallographer.
• February 2 – Bartel Leendert van der Waerden (died 1996), Dutch mathematician.^[14]
• February 22 – Frank P. Ramsey (died 1930), English mathematician.
• April 6 – "Doc" Harold Eugene Edgerton ("Papa Flash", died 1990), American electrical engineer.
• April 9 – Gregory Goodwin Pincus (died 1967), American biologist, co-inventor of the combined oral contraceptive pill.
• April 25 – Andrey Kolmogorov (died 1987), Russian mathematician.
• May 2 – Benjamin Spock (died 1998), American pediatrician and writer.
• June 14 – Alonzo Church (died 1995), American mathematician.
• July 16 – Irmgard Flügge-Lotz (died 1974), German-American mathematician and aerospace engineer
• August 7 – Louis Leakey (died 1972), British East African paleoanthropologist.
• October 4 – Cyril Stanley Smith (died 1992), English-born metallurgist.
• October 5 – M. King Hubbert (died 1989), American geophysicist.
• October 10 – Bei Shizhang (died 2009), Chinese biologist and founder of the Institute of Biophysics, Chinese Academy of Sciences.
• November 7 – Konrad Lorenz (died 1989), Austrian zoologist.
• November 27 – Lars Onsager (died 1976), Norwegian-born chemist.
• December 19 – George Davis Snell (died 1996), American mouse geneticist and basic transplant immunologist.^[15]
• December 28 – John von Neumann (died 1957), Hungarian-born mathematician.

• February 1 – Sir George Stokes, 1st Baronet (born 1819), Anglo-Irish mathematician and physicist.
• February 7 – James Glaisher (born 1809), English meteorologist and balloonist.
• March 28 – Émile Baudot (born 1845), French telegraph engineer.
• April 28 – J. Willard Gibbs (born 1839), American physical chemist.
• June 14 – Carl Gegenbaur (born 1826), German anatomist.^[16]
• July 21 – Henri Alexis Brialmont (born 1821), Belgian military engineer.
• August 2 – Edmond Nocard (born 1850), French veterinarian and microbiologist.
• August 27 – Kusumoto Ine (born 1827), pioneering Japanese woman physician.
• November 8 – Vasily Dokuchaev (born 1846), Russian geologist.