Adding of antioxidants to our daily food may reduce the risk of diseases caused by free radicals as a result of oxidative stress in the human body. In this study, eight selected Kenyan medicinal plants (Terminalia brownii, Aloe secundiflora, Prunus africana, Carissa edulis, Tithonia diversifolia, Warburgia ugandensis, Croton megalocarpus and Launaea cornuta) were studied for their potential antioxidant activity. The levels of polyphenols and flavonoids were determined using standard methods. Plant parts were extracted using water and different organic solvents. Prunus africana acetone extract had the highest levels of phenolic compounds while Tithonia diversifolia water extract had the lowest amount. The antioxidant activity was highest in Terminalia brownii acetone extract and lowest in Croton megalocarpus, Diethyl ether leaves extract, respectively. This trend was followed by antioxidant potency composite index of the medicinal plant extracts. Terminalia brownii extracts had the highest antioxidant activity and potential, followed by Prunus africana extracts due to the higher total phenolic content found in the latter medicinal plants. Total phenolic content was positively correlated with FRAP, ABTS and DPPH values. Based on the antioxidant potency composite index calculated and the overall antioxidant index, it can be concluded that the extracts from T. brownii bark and P. africana bark can be recommended as a potential natural source of antioxidants appropriate for utilization in nutritional and pharmaceutical fields. Further evaluation of the bioactive compounds and antioxidant activities in living models need to be investigated.