The ethanol extracts of the leaves of Ocimum gratissimum, Vitex doniana, Carica papaya and Peristrophe bicalyculata were assessed for antioxidant activities by the use of 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical assay. The reducing potentials of these plants were also evaluated. The phytochemical screenings of the medicinal plants were equally carried out. The percentage antioxidant activity values for the plants are: 60.0 ± 1.05%, 60.8 ± 1.28%, 62.4 ± 1.28% and 75.7 ± 2.60% for O. gratissimum, V. doniana, C. papaya and P. bicalyculata respectively. These values were dose dependent and statistically significant at P< 0.05 (ANOVA). The results indicated that P. bicalyculata has the highest antioxidant activity value of 75.7 ± 2.60% while O. gratissimum has the least value 60.0 ± 1.05%. The percentage antioxidant activities of the plants were comparable to the standards used, ascorbic acid and a-tocopherol which were found to be 86.7 ± 1.08% and 97.2 ± 1.06% respectively. The reducing potentials of the plants were found to be proportionally correlated to the antioxidant activities of the plants. Phytochemical screenings revealed the presence of flavonoids, saponins, C. glycosides, steroids, alkaloids, tannins, anthraquinones, terpenoids and carbonhydrates in the medicinal plants.