The Karasuk (Russian: Карасук) is a river in Novosibirsk Oblast, Russia. It is 531 kilometres (330 mi) long, with a drainage basin of 11,300 square kilometres (4,400 sq mi).

The source region of the Karasuk River was declared a special protected area on 26 March 2007.

The Karasuk begins some 100 kilometres (62 mi) southwest of Novosibirsk, at 190 metres (620 ft) above sea level. It flows in a southwesterly direction through a wide valley in the southern part of the Baraba Steppe, and terminates in an endorheic basin of small lakes and swamps at an elevation of 105 metres (344 ft), at the border with Kazakhstan. At high water levels some water will flow through the river Chuman (Чуман) to the Burla (Бурла), which branches from the main river towards the south, east of the town of Karasuk. Yet more water will branches off towards the north, via the Baganyonok River branch (Russian: Баганёнок), to the Bagan River. The Karasuk has no major tributaries, but there are lakes in his basin, such as Astrodym.

At the river's lower reaches lies the town and railway hub of Karasuk, named after the river.

• List of rivers of Russia