The contamination of aquatic habitats has become a serious problem for sustainability of the fisheries sector in Pakistan. Among different pollutants, heavy metals are very toxic. Their toxicity can be assessed by using antioxidant enzymes as biomarkers. These enzymes protect the living organisms from the oxidative stress caused by the heavy metals. Therefore, the effect of lead chloride (PbCl2) on the peroxidase enzyme activity in the tissues (liver and kidney) of Cirrhinamrigala was investigated. Four groups of Cirrhinamrigala were exposed, separately, to 96-hr LC50 concentration of PbCl2 along with its sub-lethal concentrations, viz.2/3rd, 1/4th and 1/5th for a period of 30 days. Another group of fish was kept in metal free media as a control. After 30 days, fish were dissected and their liver and kidney isolated and preserved for enzyme assay. Peroxidase activity in the tissues of PbCl2 exposed Cirrhinamrigala was compared with the control group. Results revealed that the activity of peroxidase enzyme in fish organs increased significantly (p