Oxidative stress has been shown to play an important role in the development of anaemia in malaria. The antioxidant activities of four medicinal plants traditionally used in the treatment of malaria were determined. The ethanolic extracts of the leaves of Vitex negundo, rhizomes of Acorus calamus, leaves of Euphorbia hirta and roots of Coleus forskohlii were used in the present study. The plants were screened for the presence of phytochemicals and, their effect on 2,2-Diphenyl-1-picryl-hydrazyl radical (DPPH) was used to determine their free radical scavenging activity. Phytochemical screening of the plants showed the presence of flavonoids, terpenoids, saponins, tannins and reducing sugars. The crude extract of the Euphorbia hirta, Vitex negundo, Acorus calamus and Coleus forskohlii showed maximum inhibition as 86.1% at 0.5mg/ml 78.4% at 1 mg/ml , 79.6% at 5mg/ml and71.7% at 5 mg/ml respectively which is comparable with vitamin C at the same concentrations. Vitex negundo being the most potent. The free radical scavenging (antioxidant) activities of these plants probably contribute to the effectiveness of the above plants in malaria therapy.