Chagan (Чага́н) was a Soviet underground nuclear test conducted at the Semipalatinsk Test Site on January 15, 1965.

The Semipalatinsk Test Site, also known as "The Polygon", was the primary testing venue for the Soviet Union's nuclear weapons. It is located in Zhanasemey District, Abai Region, Kazakhstan, south of the valley of the Irtysh River. The test site was part of the former Kazakh SSR. The scientific buildings for the test site were located around 150 km (93 mi) west of the town of Semipalatinsk, later renamed Semey, near the border of East Kazakhstan Region and Pavlodar Region. Most of the nuclear tests taking place at various sites further to the west and the south, some as far as into Karagandy Region.