Dioctyl phthalate (DOP) is widely used in plastic, medical devices and personal care product at various concentrations. Therefore a study was designed to determine the acute toxicity of DOP on haematological and biochemical parameters in fish, Clarias batrachus. Fishes were exposed to sublethal concentration of DOP 2.9ml/l and the alteration of haematological and biochemical parameters were studied at the end of 30 days. During the above treatment period the parameters like RBC, haemoglobin and Alanine aminotransferase(ALT) level decreased while WBC and serum enzyme like Aspartate aminotransferase(AST); Alkaline phosphatase(ALP) level increased.