The zooplankton composition of Lake Ladik, located in Samsun Province in northern Turkey, was investigated monthly between November 2009 and October 2010. Some physicochemical parameters such as temperature of surface water, pH, dissolved oxygen, salinity, conductivity, and total dissolved solids were also evaluated. A total of 29 zooplankton species were identified. These species were represented by three main groups: Rotifera (59%), Cladocera (24%), and Copepoda (17%). The maximum and minimum numbers of species were found in July and October, respectively. Bosmina longirostris, Keratella quadrata, Asplanchna priodonta, Cyclops abyssorum, Polyarthra dolichoptera, Brachionus calyciflorus, Keratella cochlearis, Brachionus angularis, and Chydorus sphaericus were the dominant species of the lake. According to the Brachionus: Trichocerca quotient (Q(B/T)), the trophic level of the lake is eutrophic.