The Qaidam Basin (NW China) at the northern margin of the Tibetan Plateau is one of the driest places on Earth with mean annual precipitation not exceeding 25 mm in the western central part. Flat salt plains and wind-shaped hills characterise the bare ground over thousands of square kilometres. In contrast to present-day conditions, remnants of ancient shorelines in high positions identified by Chen and Bowler (1986) and Hövermann and Süssenberger (1986) about 20 years ago herald of a former large lake but were not investigated further till now. Here we present the results of microfossil analysis and optically stimulated luminescence (OSL) as well as uranium-series (TIMS) dating of sediments from a thick sequence of predominantly lake deposits in the eastern central Qaidam Basin. Based on abundant ostracod (micro-crustacean) shells from this sequence, we infer that a large lake of several metres depth at least maintained primarily fresh to oligohaline conditions in the late Middle Pleistocene.