Indiscriminate use of pesticides has elevated the risk of contamination of environment and aquatic habitat. Considering the above fact, the present study has been under taken to investigate the alteration of some blood parameters of freshwater teleost Mystus vittatus after chronic exposure to sublethal concentrations of Metasystox (4 ppm.) and Sevin (7 ppm.) individually. The main alterations observed in certain haematological parameters were clotting time (CT), erythrocyte sedimentation rate (ESR), haemoglobin percentage (Hb%), red blood corpuscles (RBCs), white blood corpuscles (WBCs), pack cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC). Alterations in organic constituents of blood, such as glucose, blood urea, total plasma protein and cholesterol, and in inorganic constituents, such as calcium, iron, magnesium, and phosphorus, were also studied. Alteration of enzymes such as glucose-6-phosphatase (G-6-pase), fructose-1-6-diphosphatase (F-1-6-dipase), serum glutamic oxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT) were also studied, so that the changes in the blood biochemistry due to the pesticidal stress could be understood. Results indicated that CT, WBCs, MCH, MCHC, glucose, blood urea, cholesterol, magnesium and SGOT were increased, whereas other parameters were found to be decreased in both cases. Possible reasons for the above elevation are discussed in the light of available literature.