Omega-3 essential fatty acids (omega-3 EFA) contains eicosapentaenoic acid and docosahexaenoic acid (DHA). DHA is one of the building structures of membrane phospholipids of brain and necessary for continuity of neuronal functions. omega-3 EFA has been suggested to be protective against neuropsychiatric disorders including schizophrenia. This study proposed to assess the changes in superoxide dismutase (SOD), xanthine oxidase (XO), malondialdehyde (MDA), and nitric oxide (NO) in the hippocampus of rats fed with omega-3 EFA diet (0.4 g/kg/day) for 30 days. Eight control rats and nine rats fed with omega-3 EFA were decapitated under ether anesthesia, and hippocampus was removed immediately.