Wetlands are one of the most productive ecosystems. Thay are important both ecologically and economically as thay serve as breeding, feeding and nursery fish grounds for many aquatic organisms including fish. Forthermore, thay support the wildlife such as migratory birds. One of the important group of living organisms is zooplankton. Thay are basis for food web in aquatic ecosystems and transfer energy from microalgae to the higher throphic levels. Zooplanktons as first consumers are a suitable live food for the aquatic larvae such as fish, due to small size, planktonic nature, highly reproductive rate, valuable amino acid and fatty acid profile, better digestion and highly growth rate. Therefore, these creatures are important for aquaculture industry as live food and also as ecological indexes for monitoring of aquatic ecosystems. Although there are many report on amino acid profile of different zooplankton groups from separated geographical location, information on amino acid composition of mixed zooplankton from Iranian aquatic ecosystems are scarce. The objectives of this study were to identify zooplankton species, determine biomass and density of zooplankton, measurement of amino acids composition of freshwater zooplankton in Hanna wetland (latitude= 31 ? 13? N, longitude= 52 ? 46 ? E, altitude= 2300m) during four season. Seasonal field samplings were carried out at middle of each season for one-year period from May 2007 to Febuary 2008. The zooplankton samples were collected by vertical haul using plankton net (140 ?m, and diameter of 25 cm) from three sites in the Hanna wetland. For amino acid measurement zooplankton samples were initially freez-dried and then subjected to HPLC (High Performance Liquid Chromatography). Results showed that there is no significant differences the biomass of zooplankton amples between 3 sites (P 0.05), the highest in site 3 (82.19mg/m 3 )and the lowest in site 2 (56.9 mg/m 3 ). The total density of cladocerans was highest in spring (47.62 ind./L) including four species of Daphnia longispina , D. dubia , D. pulex and Moina macrocopa . The identified copepod species were all belong to cyclopoids, with the highest density observed in fall (80.38 ind./L). The abundance of cladocerans and copepods in mixed zooplankton population were different. The maximum abundance of cladocerans was observed in spring (74.37 % in population) while the abundance of copepods were the highest in summer (72.52 % in population) and fall (72.77 % in population). The protein contents in zooplankton were 58.31%, 54.25%, 55.6% and 53.9% dry weight for spring, summer, fall and winter respectively.