Cleome monophylla is a common weed in cultivated land in hills, Ethanolic extract of Cleome monophylla was subjected to in vitro antioxidant assays such as 2, 2-diphenyl-1-picryl hydrazyl radical (DPPH), Super oxide radicals (SOS) and Nitric oxide radicals (NOS). Scavenging activities of the DPPH radical by the ethanolic extract of Cleome monophylla was found to be moderate as compared to the standard ascorbic acid. The IC50 value of plant extract was 81.42 µg/ml. The superoxide radical scavenging ability of ethanol extract of Cleome monophylla (49.88 µg/ml as IC50) was competent and slightly lower than standard ascorbic acid (24.19 µg/ml). The ethanol extract of Cleome monophylla showed a high forceful free radical scavenging activity in the nitric oxide assay at 40 µg/ml concentration.