Mussels are used as bio-indicators to evaluate the toxic effects of chemical pollutants in freshwater organisms, especially heavy metals, representing an important tool for bio-monitoring environmental pollution in aquatic environment. Antioxidant defence enzymes play an important role in cellular antioxidant defence systems and protect from oxidative damage by reactive oxygen species (ROS). Zinc is an environmental pollutant that causes damage to biological systems. The enzyme activities of catalase was studied in the digestive gland of the freshwater mussels, Lamellidensconsobrinus under the two groups. Group A was maintained as control; group B mussels were exposed to chronic LC50/10 dose of zinc sulphate (0.34 ppm) up to 21 days. After 21 days investigate the potential use of the antioxidant defence enzymes against heavy metal pollution in freshwater mussels, Lamellidensconsobrinus as biomarkers of oxidative stress. Catalase activities in digestive gland of control and experimental mussels from A and B groups respectively were estimated after 7, 14 and 21 days. CAT showed a significant increased activity with increasing exposure period of heavy metal salts, ZnSO4 but decrease increase the chronic period of exposure. Means catalase activity was highest in mussels from treatments exposed to the heavy metal concentrations as compared to control group of mussels. However, the lowest concentration of CAT activity after 14 and 21 days exposure to zinc. Catalase activity (CAT) was measured following the decrease of absorbance at 240 nm due to H2O2 consumption (Luck H.1974).