The free radical scavenging potential of roots of Thespesia lampas Dalz and Gibs was studied by different antioxidant models. Free radicals are implicated for more than 80 diseases including Diabetes mellitus, arthritis, cancer, ageing etc. In the treatment of theses diseases, antioxidant therapy has gained an utmost importance. Current research is directed towards finding naturally occurring antioxidant of plant origin. In Indian system of medicine, Thespesia lampas is an important medicinal plant and its root juice has been used in various ailments and as health tonic. To understand the mechanisms of pharmacological actions, the in vitro antioxidant activity of aqueous extract of Thespesia lampas was investigated for the activity of scavenging superoxide anion radicals, nitric oxide radical and lipid peroxidation assay. In all the testing, a significant correlation existed between concentrations of the extract and percentage inhibition of free radicals, metal chelating, reducing power or inhibition of lipid peroxidation. These results clearly indicate that Thespesia lampas is effective against free radical mediated diseases. © 2010 Elsevier B.V., All rights reserved.; MEDLINE® is the source for the MeSH terms of this document.