December 27 is the 361st day of the year (362nd in leap years) in the Gregorian calendar. There are four days remaining until the end of the year.
- 537 – The Hagia Sophia is completed.
- 1922 – Japanese aircraft carrier Hōshō becomes the first purpose built aircraft carrier to be commissioned in the world.
- 1945 – The World Bank and International Monetary Fund are created with the signing of an agreement by 29 nations
- 1966 – The Cave of Swallows, the largest known cave shaft in the world, is discovered in Aquismón, San Luis Potosí, Mexico.
- 1968 – Apollo Program: Apollo 8 splashes down in the Pacific Ocean, ending the first orbital manned mission to the Moon.
- 1978 – Spain becomes a democracy after 40 years of dictatorship.
- 2001 – The People's Republic of China is granted permanent normal trade relations with the United States.
- 2007 – Former Pakistani Prime Minister Benazir Bhutto is assassinated in a shooting incident.