- Jan 2 American anarcho-syndicalist union known as the Industrial Workers of the World forms
- Jan 22 In St Petersburg, Russia, a large demonstration of workers led by Father Gapon, march to the Winter Palace with a petition to the Tsar; troops fire on protesters in what becomes known as 'Bloody Sunday'
- Mar 17 Albert Einstein finishes his scientific paper detailing his Quantum Theory of Light, one of the foundations of modern physics
- Jun 30 In Russia, the "Potemkin" arrives at Odessa, where sailors take the bodies of dead crewman ashore; sailors join civilians in revolutionary actions of the '1905 Revolution'
- Jul 29 US Secretary of State William Howard Taft makes secret agreement with Japanese Prime Minister Katsura agreeing to Japanese free rein in Korea in return for non-interference with the US in the Philippines
- Sep 27 The physics journal Annalen der Physik publishes Albert Einstein's paper "Does the Inertia of a Body Depend Upon Its Energy Content?", introducing the equation E=mc².
- Oct 30 "October Manifesto" Russian Tsar Nicholas II grants civil liberties and accepts the first Duma (Parliament)
World's largest diamond, the 3,106-carat Cullinan, is found in South Africa
On January 26, 1905