The present study examined the changes occurring in the pro phenoloxidase system and antioxidant defence status in haemolymph, hepatopancreas and muscle tissue of white spot syndrome virus (WSSV) infected Penaeus monodon. Tiger shrimps (P. monodon) were infected with white spot virus by intramuscular injection of the virus inoculum. Levels of lipid peroxides and the activities of phenoloxidase, glutathione-dependent antioxidant enzymes [glutathione peroxidase (GPX), glutathione-S-transferase (GST)] and antiperoxidative enzymes [superoxide dismutase (SOD) and catalase (CAT)] were determined. WSSV infection induced a significant increase in lipid peroxidation in haemolymph, muscle and hepatopancreas of experimental P. monodon compared to normal controls. This was paralleled by significant reduction in the activities of phenol oxidase, glutathione-dependent antioxidant enzymes and antiperoxidative enzymes. The results of the present study indicate that the tissue antioxidant defence system in WSSV infected P. monodon is operating at a lower rate, which ultimately resulted in the failure of counteraction of free radicals, leading to oxidative stress as evidenced by the increased level of lipid peroxidation.