This study was carried out to determine the effect of methanol leaf extract of Dryopteris filix-mas on catalase (an antioxidant) activity and malondialdehyde (an oxidative stress marker) levels in brain of wistar rats. Methanol extract of Dryopteris filix-mas was prepared by Soxhlet extraction. Twenty (20) adults male wistar rats were used for this study. The animals were grouped into four groups; 1 (normal control); 2 (administered 100mg/kg of Dryopteris filix methanol leaf extract) and 3 (administered 250mg/kg of Dryopteris filix methanol leaf extract); 4 (Administered 500mg/kg of Dryopteris filix methanol leaf extract). The rats were so treated and after 21 days, were sacrificed. The brain of the rats was harvested and used to prepare brain tissue homogenates for the biochemical assay of catalase and MDA using standard procedures. Results obtained show that the varying doses of the plant extract caused a dose dependent increase in catalase activity when compared to the control group. However, the increases were found to be statistically insignificant (p>0.05). Administration of 100mg/kg of the plant extract slightly decreased MDA level, while 250mg/kg and 500mg/kg slightly increased MDA levels in brain of the experimental animals after the 21days treatment period when compared to the control group. However, these observed changes in MDA levels were found to be statistically insignificant (p>0.05). The results of this study shows that the different doses of the plant extract did not cause significant oxidative damage to the brain of the experimental animals.