Zhamantuz () is a salt lake in the Aktogay District, Pavlodar Region, Kazakhstan.
The lake lies to the east of Barlybai village. The area surrounding Zhamantuz is used for livestock grazing.
Zhamantuz is an endorheic lake of the Ishim Plain, at the southern end of the West Siberian Plain. It is part of the Irtysh river basin. The lake lies at an elevation of . The Irtysh flows to the northeast of the lake.
Zhamantuz has a roughly hourglass shape, with a smaller northern part connected to the southern through a narrow sound. The lake freezes in late November and stays under ice until the second half of March. It usually dries in the summer. There are a number of other lakes in its vicinity, such as Koserin to the east, Aralsor to the NNW, Karakaska to the WSW, and Taikonyr to the southeast. to the SSW lies larger lake Zhalauly.
Zhamantuz is known as a "dead lake" () in Kazakh. Reeds grow in stretches of the shore. The lake is used for watering cattle in the spring.