Tacheng (Qoqek) or Chöchek is a county-level city (1994 est. pop. 56,400) and the capital of Tacheng Prefecture, in northern Ili Kazakh Autonomous Prefecture, Xinjiang, China.
The city was sometimes called Tarbaghatay or Tarbagatai (Mongolian: 'having marmots') and was once known in European languages as Chuguchak (based on its name in Turkic languages). The current Uyghur name is Qöqäk Xäĥri.
It is located in the Dzungarian basin, some 10 km from the Kazakhstan border. Long a major center for trade with Central Asia, it is an agricultural hub. Its industries include food processing, textiles, and utilities.
The city suffered much destruction in 1865, during the fighting between the Qing forces and the Dungan and Uyghur rebels.