Indian major carp Catla catla were exposed to sublethal concentration of monocrotophos to determine the role of pesticide on fish physiology. Fish were exposed to sublethal concentration (0.0250mg/l) for acute (5 days) and subchronic (30 days). Blood biochemical parameters such as Total protein, Total glucose, Urea nitrogen, Creatinine, Cholestrol, Triglycerides, Bilirubin, AST and ALT levels were estimated in the control and experimental fishes. Significant changes in the biochemical parameters were obtained in the experimental group compared with the control. The total protein and total glucose decreased in the acute and sub chronic exposures compared with control; where as a significant increase in urea nitrogen, creatinine, bilirubin, cholesterol, triglycerides, AST and ALT levels were noticed. The changes in the biochemical profiles shows monocrotophos induce alterations in the blood, which may be used as an index for the toxic role of pesticide on the aquatic organisms.