The Köksu () 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 long and has a basin area of .
It is the largest river in the Koksu District and gives its name to the district.
Several hydro-electric projects are located along the river, including the Kyzylbulak Hydroelectric Power Plant and Kyzylkungei Hydroelectric Power Plant.