Extracts of 42 medicinal plants used for the treatment of anaemia, diabetes, AIDS, malaria and obesity were screened for phytochemical substances and antioxidant potentials. The plant extracts were prepared as hydrolysed (for total antioxidant) and non-hydrolysed (for free antioxidant). Extracts were analysed using three different assay methods for antioxidant analysis: Folin (Folin Ciocalteu reagent), FRAP (Ferric Reducing Antioxidant Power) and DPPH (1,1-diphenyl-2-picrylhydrazyl). The leaves of Alchornea cordifolia showed the highest antioxidant properties as determined by both Folin and FRAP free antioxidant, followed by Dacryodes edulis and Ocimum basilicum in FRAP and by Dacryodes edulis, Harungana madagascariensis for Folin and DPPH method. For total antioxidant activity, Alchornea cordifolia was ranked first followed by Dacryodes edulis, Harungana madagascariensis, Ocimum basilicum for the FRAP method while for the Folin method Harungana madagascariensis occupied the first position followed by Cylicodiscus gabunensis, Ocimum basilicum, Coleus coprosifolius, Alchornea cordifolia, Dacryodes edulis. All the plants show some antioxidant activity irrespective of the method used. The phytochemical studies revealed the presents of important bioactive constituents with antioxidant activity that may have some medicinal properties.