Acetone extracts of the three medicinal plants Sida cardifolia, Phyllanthus amarus and Adathoda vasica were assessed for phytochemical components qualitatively and quantitatively and antioxidant activity. The results revealed that all the three contained alkaloids, carbohydrates, flavonoids, tannins, anthocyanins, steroids and phenols. Saponins were absent in all the three extracts. Sida cardifolia with 1.53mg and 7.09mg GA equivalent/g of extract powder showed maximum amount of Phenolics and flavonoids.The total sugars and proanthocyanidins was maximum in Phyllanthus amarus with 8.45ug glucose equivalent/g of extract powder and 10.84mg GA equivalent/g of extract powder. Tannin content was found to be high in Adathoda vasica with 11.07mg GA equivalent/g of extract powder. Sida cardifolia acetone leaf extract showed the highest reducing power activity, Free radical scavenging potential and inhibition of lipid peroxidation. INTRODUCTION: In a healthy body prooxidants and antioxidants maintain a ratio and a shift in this ratio towards prooxidants gives rise to oxidative stress. This oxidative stress may be either mild or severe depending on the extent of shift. This causes several diseases such as cardiovascular diseases, neurological diseases, renal diseases, diabetes, skin diseases, ageing, respiratory diseases and inflammatory problems 1, 2. Over 70 degenerative diseases are due to oxidative stress. These free radicals are produced from two important sources, cellular metabolism and environmental sources.