The Koksu (Kazakh: Көксу, Köksu; su meaning "river") is a river of the Balkhash-Alakol Basin, Kazakhstan. It flows within Almaty Region, in the historical Semirechye region, from the western slopes of the Dzungarian Alatau. The river is 205 kilometres (127 mi) long and has a basin area of 4,670 square kilometres (1,800 sq mi).

It is the largest river in the Koksu District, named after it.

Several hydro-electric projects are located along the river including the Kyzylbulak Hydroelectric Power Plant and Kyzylkungei Hydroelectric Power Plant.