Zhamantuz () is a salt lake in the Ualikhanov District, North Kazakhstan Region, Kazakhstan.
The lake lies to the east of Balkabek, an abandoned village. The Pavlodar Region border lies to the east of the eastern lakeshore. The area surrounding lake Zhamantuz is used for livestock grazing.
Zhamantuz is an endorheic lake part of the Sileti river basin. It lies at an elevation of . A broad headland extends eastwards in the northern half of the western shore. The Sileti flows to the east of the lake.
The long Semizbay river flows from the west into the western shore. Lake Zhamantuz freezes in November and stays under ice until April. The southern end of larger lake Siletiteniz lies to the northeast, and lake Zhaksytuz to the SSE.