In the catchment area of Lake Uvs Nuur (Northwest Mongolia) samples of branchiopods and copepods were collected in 15 different lentic water bodies. The waters differ in respect to water chemistry, salt content (fresh, saline), water depth (shallow, deep), catchment area and surrounding landscape and vegetation (semi-desert, steppe areas, alpine regions). 38 species of cladocerans and 16 species of copepods were found. The salt waters (> 0.5 g/l up to 20 g/l) housed altogether 31 species; the fresh waters (< 0.5 g/l) had a distinctly larger number of species (40 species). The populated waters are briefly characterized with regard to morphometry, macrophytes and fish stock. 12 species – 8 Cladocera and 4 Copepoda – have not previously been recorded from Mongolia. Morphological and taxonomical remarks are made on certain species. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)