Abstract: Background and Objective: Local consumers of whole palm fruit extract claim that it is rich in nutraceutical properties. This claim has not been validated as there is no scientific evidence or data to take back up. This study was designed to investigate in vitro antioxidant activity of the aqueous extracts of palm fruits and their effects on the antioxidant parameters of male Wistar albino rats with a view of improving human health. Materials and Methods: The acute toxicity study was carried out with 18 male Wistar albino mice while 45 male Wistar albino rats were used for the study of the effects on antioxidant parameters. The rats were grouped into 5 groups: Group 1 serving as normal control and received 2 mL kg–1 b.wt., of normal saline. Five rats each in group 2-5 received 100, 200, 400 and 600 mg kg–1 b.wt., of the fresh and fermented extracts of palm fruits respectively for 28 days and the rats were sacrificed on the day 29. The data obtained were statistically analyzed using one way analysis of variance and t-test. Results: The aqueous extracts were relatively safe as their administration resulted to no death or adverse reactions. The extracts possess high total antioxidant capacity, ferric reducing antioxidant power and effectively inhibited lipid peroxidation depicted by low concentrations of thiobarbituric acid and malondialdehyde. In addition, the extracts exhibited a dose dependent increase in percentage inhibition of 1,1-Diphenyl-2-picrylhydrazyl radicals. The extracts caused a dose dependent significant (p<0.05) decrease in catalase activity and significant increase in superoxide dismutase activity of all the rats administered the extracts. Whereas, the fermented extract administration led to significant (p<0.05) dose dependent increase in myeloperoxidase and glutathione peroxidase activity in the rats, the fresh extract caused significant (p<0.05) decrease in myeloperoxidase and glutathione activity of group 2 rats and a dose dependent increase in groups 3-5. Conclusion: These findings suggest that the extracts possess antioxidant properties which could effectively prevent oxidative stress, lipid peroxidation, ameliorate damage and associated health consequences resulting from activity of excess free radicals, if taking in adequate concentration.