The present work is focused on the taxonomic composition of zooplankton in Ulaagchny Khar, Zhaakhan and Baga lakes (Western Mongolia). Several species (Synchaeta stylata, Synchaeta oblonga, Polyarthra luminosa, Pleuroxus annandalei, Cyclops scutifer, Eucyclops dumonti, Eucyclops arcanus) rarely found in Central Asia but abundant in the lakes under study were identified. Morphological features of Cyclops scutifer, Pleuroxus annandalei and Daphnia turbinata are briefly described, the latter was registered in Mongolia for the first time. The species composition of rotifers, cyclops and cladocerans was supplemented by new data. Examination of zooplankton, seasonal variations of saprobity and diversity index provided evidence on slight pollution of these lakes.