Abstract: The current study was designed to investigate the behavioural and biochemical changes induced by endosulfan in brain, gills, liver and muscle of rohu, Labeo rohita. Behavioural changes observed after exposing fish to LC50 of endosulfan, were erratic swimming, jumping, loss of equilibrium and balance, hyperactivity, increased air gulping and surface activity. These changes were observed to be more pronounced with length of exposure time. Longer exposure made the fish lethargic, with the lesser operculur beat, adopted a vertical position sometimes and motionless state before dying. Internal hemorrhage was conspicuous. A time dependent decrease in total protein contents and increase in antioxidant enzymes, including catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), glutathione reductase (GR), reduced glutathione (GSH), glutathione peroxidase (GSH-Px) and glutathione-s-transferase (GST) was observed in the brain, gills, liver and muscles of rohu. A time dependent increase in malondialdehyde (MDA) concentration was also observed in different tissues. The current study reports endosulfan as highly toxic to L. rohita. Its indiscriminate use should be controlled in order to conserve the population of rohu and other Cyprinids in natural aquatic systems.