The Nanking Massacre, also known as the Rape of Nanking, was an episode of mass murder and mass rape committed by Japanese troops against the residents of Nanking (current official spelling: Nanjing) during the Second Sino-Japanese War.

The massacre occurred during a six-week period starting from December 13, 1937, the day that the Japanese captured Nanking, which was then the Chinese capital (see Republic of China). During this period, between 40,000 to over 300,000 (estimates vary) Chinese civilians and disarmed combatants were murdered by soldiers of the Imperial Japanese Army.

Widespread rape and looting also occurred. Several of the key perpetrators of the atrocities, at the time labelled as war crimes, were later tried and found guilty at the International Military Tribunal of the Far East and the Nanjing War Crimes Tribunal, and were executed. Another key perpetrator, Prince Asaka, a member of the Imperial Family, escaped prosecution by having earlier been granted immunity by the Allies.

Since most Japanese military records on the killings were deliberately kept secret or destroyed shortly after the surrender of Japan in 1945, historians have not been able to accurately estimate the death toll of the massacre.

The International Military Tribunal of the Far East estimated in 1948 that over 200,000 Chinese were killed in the incident.

China's official estimate is more than 300,000 dead based on the evaluation of the Nanjing War Crimes Tribunal in 1947. The death toll has been actively contested among scholars since the 1980s, with typical estimates ranging from 40,000 to over 300,000.

The event remains a contentious political issue, as various aspects of it have been disputed by historical revisionists and Japanese nationalists, who claim that the massacre has been either exaggerated or wholly fabricated for propaganda purposes.

As a result of the nationalist efforts to deny or rationalize the war crimes, the controversy surrounding the massacre remains a stumbling block in Sino-Japanese relations, as well as Japanese relations with other Asia-Pacific nations such as South Korea and the Philippines.