In recent years, development of nanotechnology as well as the toxicity potential of nanomaterials on the environment has received much attention. In order to assess the potential toxic impact of nanoparticles on aquatic environments, we used three kinds of nanoparticles, including titanium dioxide (TiO2), copper oxide (CuO), and zinc oxide (ZnO) on an aquatic model species, Daphnia magna. In fact, Daphnia magna was exposed to different concentrations for 24, 48, 72, and 96 h at 20-25°C. All the important water quality parameters, such as temperature, pH, and dissolved oxygen (DO) were controlled to meet the standard requirements during the experiment. The LC50 values for 24, 48, 72, and 96 h were estimated statistically using Probit methods. The LC50 48 h values for TiO2, CuO, and ZnO were 171.88 mg/l, 6.62 mg/l, and 3.23 mg/l, respectively.