Toxicological effect of distillery effluent in the catfish, Mystus vittatus was investigated in the present study. Distillery effluent discharged from distillery unit of Balrampur Chini mill, Balrampur, U.P. was collected and healthy test fish of 7.0-8.0 cm in length and weighting 8.0-9.0 gm were collected from local fresh waterbodies were exposed to a sublethal concentrations (2.5% and 3.0% of LC50 value i.e., 3.38 %) of the effluent for a period of 15 and 30 days. The histological changes in the RBC morphology in the effluent treated fish and the control group were compared. There was significant reduction in the mean length, breadth and area of erythrocytes in distillery effluent exposed fish. The study revealed marked changes such as membrane disintegration, Anisocytosis, poikilocytosis, double nuclei and rouleaux development, etc. are noticed in the blood tissues of the effluent exposed fish.