The seed of Phaseolus calcaratus Roxburgh (PHCR) is traditionally used for anti-pyretic and antiinflammatory effects. Although these effects are believed to be related to its antioxidant potential, little information is available for the mechanisms by which PHCR seed might scavenge free radicals or otherwise act as an antioxidant. In the present study, we purified some fractions from the ethanol extract of PHCR seed and evaluated each fraction`s ability to scavenge free radicals generated by cell-free systems. We also identified active compound that is putatively responsible for free radical scavenging by analyzing NMR spectra. PHCR samples exhibited a concentration-dependent radical scavenging activity against hydroxyl radicals, superoxide anions, and DPPH radicals. Of the samples tested, a methanol-eluted sub-fraction from the PHCR extract, named FF4, scavenged these radicals more effectively than the other fractions. We identified catechin-7-O-β-Dglucopyranoside as the active compound responsible for free radical scavenging potential of FF4.