Water pollution is the burning issue nowadays all over the world. Aquatic ecosystems are frequently contaminated with different toxicants through anthropogenic activities, and some of concentrations. Heavy metals are important inducers of oxidative stress in aquatic animals, promoting formation of reactive oxygen species. The water flea Daphnia magna is the most commonly used zooplankton in toxicological tests, due to short doubling time, high sensitivity, and simplicity; therefore, it was used as an indicator in this study. This study aimed to evaluate the effects of Heavy metals on the total protein and the antioxidant biomarkers in freshwater cladoceran, Daphnia magna. The collected cladocerans Daphnia magna, have been continuously reared in Hydrobiology Laboratory at the Water Pollution Research Dept., National Research Center in the synthetic freshwater medium. The animals were fed three times a week with 14X107 coenobia /ml of the green microalga Scenedesmus obliquus and were kept at a temperature 22±2°C. Specimens of the investigated species were classified into five experimental groups (390 animals per each). The first group was the control (untreated group) and the other four groups were treated. The four treated groups were subjected to different concentrations (LC10, LC20, LC40, and LC50 or (30.70, 40.7, 59.3, and 69.7); (192.57, 215.36, 250.11 and 266.75) µg/L of Cu and Cd for 48 hours respectively. After 48 hours of exposure, the activity of antioxidant enzymes (catalase CAT and Glutathione reduced GSH) and total protein, were determined for each experimental group. Results showed a highly significant decrease in the activity of total protein while the activity of antioxidant enzymes (catalase CAT and Glutathione reduced GSH) showed highly significant increase after exposure to Cu and Cd for 48hours.