The toxic impact of organochlorine pesticide endosulfan was estimated on Indian channel catfish Clarias batrachus (Linn.). The most exposed organ gills were examined under Scanning Electron Microscope (SEM) of the treated and control fishes. The hematocytes were also examined under SEM. The blood biochemistry for alkaline phosphatase, acid phosphatase, C-reactive protein and cortisol were also investigated. The experiment shown major alterations in the blood biochemistry and ultrastructure of gill and blood cells.