This study was designed to find out the metabolic consequences of H2O2 following catalase inhibition by aminotriazole in the fat body of an Antheraea mylitta pupa. H2O2 content in the pupal fat body exhibited a decreasing trend over the experimental period (up to 48 h). However, a substantial decrease in its level was marked after 12, 24 and 48 h of treatment. The level of lipid peroxidation was elevated within 4 h of aminotriazole injection. Nevertheless, its level significantly decreased after 12, 24 and 48 h of treatment. Superoxide dismutase activity was elevated within 4 h, followed by a transient decrease in its activity at 12 h of treatment and again increased over the experimental period. Catalase activity was found to decline in the fat body within 4 h of aminotriazole treatment compared to the control. However, it was surprising to observe that there was a two-fold increase in catalase activity compared to its previous experimental group after 12 h, followed by a rapid decline in its activity at 24 h of aminotriazole injection and non-detectable catalase activity at 48 h. Ascorbic acid content was found to be elevated after 12 h of injection and maintained an increasing trend over the rest of the experimental period compared to the respective control. Despite the progressive inhibition of catalase activity beyond 12 h of treatment, H2O2 accumulation was not observed as a consequence of catalase inhibition. Hence, catalase depletion by aminotriazole involves compensatory changes in other components of the antioxidant system for the efficient removal of H2O2.