The Potpec reservoir is situated in the southwest of Serbia. It has been formed in 1977 on the Lim river and used for the electric energy production. In this paper, the results of the qualitative and quantitative analysis of zooplankton, as well as saprobiological analysis of plankton community, are presented. The sampling has been carried out in August 2004, on the three localities of free water of the lake, on three different depths, from the surface to the bottom. By the qualitative analysis of zooplankton, the presence of 38 taxa has been identified The quantitative analysis shows the domination of the species: Ploesoma truncatum Levander, Keratella cohlearis Gosse and Polyartra vulgaris Carlin (Rotatoria). Representatives of Cladocera with high population density are Moina micrura (Kurz) and Bosmina longirostris (O.F.M.), on the localities at the dam and in the central part of the reservoir, and Daphnia galeata G.O. Sars at the entrance of the reservoir. By saprobiological analysis of plankton community it has been concluded that the greatest number of indicatory organisms belongs to oligosaprobionts and beta-mesosaprobionts. The values of saprobic index varied from 1.6 at the dam (oligo-beta mesosaprobic zone), to 1.8 in the central part of the reservoir (beta mesosaprobic zone).