The aim of this study was to assess the in vitro potential of chloroform extract of Chromolaena odorata leaves The DPPH activity of the extract (0.1-5 mg/ml) was increased in a dose dependent manner, which Was found in the range of 23.48-91.61% as compared to ascorbic acid (33 69-94.10%) The IC50 values of chloroform extract in DPPH radical, hydroxyl radical, nitric oxide. ABTS radical were obtained to be 0.31, 0.43, 0.28 and 1.32 mg/ml, respectively. However, the IC50 values for the standard ascorbic acid were noted to be 0.24, 0.41, 0.23 and 1 mg/ml, respectively. Measurement of total phenolic content of the chloroform extract of C odorata was achieved using Folin-Ciocalteau reagent containing 242.2 mg/g of phenolic content, which was found significantly higher when compared to reference standard gallic acid The results obtained in this study clearly indicate that C odorata has a significant potential to use as a natural anti-oxidant agent. (C) 2009 Elsevier Ltd. All rights reserved.