Zhamantuz (Kazakh: Жамантұз) is a salt lake in the Zhangeldi District, Kostanay Region, Kazakhstan.

The lake lies 17 kilometers (11 mi) to the south of Kokalat town. The name Zhamantuz, meaning "bad salt" in the Kazakh language, is of nomadic origin.

Zhamantuz is an endorheic lake of the Turgay Depression. It is part of the Turgay river basin. The lake lies at an elevation of 111 meters (364 ft). The Turgay flows about 15 kilometers (9.3 mi) to the northwest of the lake.

Zhamantuz has an elongated shape, stretching for over 5 kilometers (3.1 mi) in a northeast–southwest direction. The lake fills yearly with rain and snow and rarely freezes in the winter. Zhamantuz is an intermittent lake that dries in the summer.

Zhamantuz is known as a "dead lake" (Kazakh: тұйық көл) in Kazakh owing to the lack of fish living in its bitter waters. Typha and Phragmites reeds grow in stretches of the lakeshore and wormwood tufts close around the basin.

• List of lakes of Kazakhstan

• Media related to Zhamantuz, Zhangeldi District at Wikimedia Commons