This study investigated the alterations in the activities of several antioxidant enzymes inthe gills of the freshwater fish Carassius auratus gibelio exposed to deltamethrin. To getthis goal, groups of 10 individuals were exposed for one, two, three, seven and fourteendays to sublethal concentration of deltamethrin (2 µg/L). Another group was used ascontrol. The activities of catalase, gluthatione peroxidase and gluthatione reductasewere significantly decreased, while the glutathione-S-transferase was up-regulated. Allfish, exposed to 2 µg/L deltamethrin revealed gills morphological alterations after 48h ofexposure which were accentuated after 14 days. In the gills hyperemia, fusion ofsecondary lamellae, epithelial layer rupture and chloride cells proliferation wereobserved. These results suggest that an immediate adaptive response to the oxidativestress appeared, demonstrating alterations in the antoxidant defense mechanism in thegills of deltamethrin intoxicated fish.