The year 1943 in science and technology involved some significant events, listed below.

• July 21 – Living specimens of Metasequoia glyptostroboides, the Dawn Redwood, previously known only as a Mesozoic fossil, are located in China.^[1]
• The University of Oxford acquires the nearby Wytham Woods which become an important centre for research into ecology in England.
• David Lack's study The Life of the Robin is published in England.

• March–December – Construction of British prototype Mark I Colossus computer, the world's first totally electronic programmable computing device, at the Post Office Research Station, Dollis Hill, to assist in cryptanalysis at Bletchley Park.^[2]
• May 17 – The United States Army contracts with the University of Pennsylvania's Moore School to develop the ENIAC.

• February 20 – The cinder cone volcano Parícutin begins to appear in Mexico, giving volcanologists an unusual opportunity to observe its complete life cycle.^[3][4][5]

• January 1 – Project Y, the Manhattan Project's secret laboratory at Los Alamos, New Mexico, for development and production of the first atomic bombs under the direction of J. Robert Oppenheimer, begins operations.

• March 23 – The drugs Vicodin and Lortab are made in Germany.
• October 19 – The antibiotic streptomycin (the first antibiotic remedy for tuberculosis) is first isolated by Albert Schatz in the laboratory of Selman Abraham Waksman at Rutgers University in the United States.^[6]
• December – Winston Churchill's recurring bacterial pneumonia is successfully treated with the sulphapyridine M&B 693, a first-generation sulphonamide antibiotic.^[7]
• A golden mould, Penicillium chrysogenum, growing on an American cantaloupe in Peoria, Illinois, is found to be ideal for mass production of penicillin.^[8]

• Abraham Maslow proposes the Hierarchy of Needs theory of psychology in his paper "A Theory of Human Motivation".

• April 16–19 – Albert Hofmann discovers the hallucinogenic properties of lysergic acid diethylamide.^[9]
• Leo Kanner of the Johns Hopkins Hospital first publicly adopts the term autism in its modern sense in English in referring to early infantile autism.^[10]
• Warren S. McCulloch and Walter Pitts publish "A Logical Calculus of the Ideas Immanent in Nervous Activity" in Bulletin of Mathematical Biophysics, considered seminal in neural network theory.^[11]
• Dr. Willem J. Kolff builds the first dialysis machine, in the occupied Netherlands.^[12]
• New Zealand-born British anaesthetist Robert Macintosh introduces his new curved laryngoscope blade for tracheal intubation.^[13][14]

• March 5 – The Gloster Meteor, the first operational military jet aircraft for the Allies of World War II, has its first test flight, in England.
• May 16–17 – Operation Chastise: British Royal Air Force attacks German dams using 'bouncing bombs' designed by Barnes Wallis.^[15]
• Lyle Goodhue and William Sullivan patent the refillable aerosol spray in the United States, for use with mosquito–repellant.^[16]
• Krueger flaps for aircraft wings are invented by Werner Krüger and evaluated in the wind tunnels in Göttingen.

• Nobel Prizes
  • Physics – Otto Stern
  • Chemistry – George de Hevesy
  • Medicine – Carl Peter Henrik Dam, Edward Adelbert Doisy

• January 14 – Ralph Steinman (died 2011), Canadian-born cell biologist, awarded Nobel Prize in Physiology or Medicine (2011).
• April 26 – Christiane Floyd, Austrian-born computer scientist.
• May 9 – Colin Pillinger (died 2014), English astrophysicist.
• May 14 – Richard Peto, English epidemiologist.
• June 6 – Richard Smalley (died 2005), American organic chemist, recipient of Nobel Prize in Chemistry (1996) for discovery of buckminsterfullerene.
• June 16 – Nancy Doe Hopkins, American molecular biologist and advocate for women in science.
• June 22 – J. Michael Kosterlitz, Scottish-born condensed matter physicist, winner of the Nobel Prize in Physics (2016).
• June 23 – Vint Cerf, American Internet pioneer.
• July 11 – Hilary Kahn (died 2007), South African-born English computer scientist.
• August 3 – Masato Sagawa, Japanese inventor.
• August 10 – Louis E. Brus, American chemist, recipient of Nobel Prize in Chemistry (2023).
• August 29 – Arthur B. McDonald, Canadian astrophysicist, recipient of Nobel Prize in Physics (2015).
• September 20 – Richard McGehee, American mathematician working on celestial mechanics.
• December 7 – Nick Katz, American mathematician.
• Mary Lake Polan, American obstetrician and gynecologist.
• Steen Willadsen, Danish-born embryologist.

• January 5 – George Washington Carver (born c.1864), African American agricultural botanist.
• January 7 – Nikola Tesla (born 1856), Croatian-born Serbian American inventor.
• January 24 – Carl Brigham (born 1890), American pioneer of psychometrics.
• January 26 – Nikolai Vavilov (born 1887), Russian plant pathologist (in prison).
• February 14 – David Hilbert (born 1862), German mathematician.
• February 20 – Ernest Guglielminetti (born 1862), Swiss physician^[17]
• February 23 – Abraham Buschke (born 1868), German Jewish dermatologist (in Theresienstadt concentration camp).
• March 2 – Gisela Januszewska (born 1867), Austrian public health physician (in Theresienstadt concentration camp).^[18]
• March 28 – Robert W. Paul (born 1869), English pioneer of cinematography.
• April 8 – Kiyotsugu Hirayama (born 1874), Japanese astronomer.
• June 26 – Karl Landsteiner (born 1868), Austrian-born American Jewish physiologist.
• July 5 – Charles Gandy (born 1872), French physician.
• July 7 – Hugh Whistler (born 1889), English ornithologist of India.
• September 23 – John Bradfield (born 1867), Australian civil engineer.
• September 30 – Carl Edvard Johansson (born 1864), Swedish metrologist.
• October 1 – Albert Stewart Meek (born 1871), English-born Australian ornithologist.
• November 14 – Frank Leverett (born 1859), American glaciologist.
• November 20 – Bertha Lamme Feicht (born 1869), American electrical engineer.