The use of pesticides rises exponentially with the industrial and agricultural development. However, these pesticides create serious threat to the non-target organisms both in terrestrial as well as aquatic ecosystems. Hazardous chemicals from industrial wastes and agricultural runoff are the main causes of water pollution. An aquatic organism mainly fish accumulates many contaminants directly through their gills and skin and indirectly via their food chain, which may cause diverse alternations in their vital organs. In the present study, effect of pentachlorophenol (PCP) on the histology of testis of a freshwater catfish Heteropneustes fossils (H. fossilis) was studied by exposing the fish to sub lethal concentration at32pg/l/day (1/10 of LC50) for a period of 14 and 28 days. Histopathological changes were observed in testis which showed shrinkage of seminiferous lobules and vacuolization in the tubular epithelium as well as in interlobular space. Histological impairment in tissues of lobules was also observed during different periods of exposure, suggesting adverse impact of PCP on testis of H. fossils.