In traditional Chinese medicine preparations, Hedyotis diffusa (HD), Hedyotis corymbosa (HC) and Mollugo pentaphylla (MP) are often used interchangeably under the name of "Peh-Hue-Juwa-Chi-Cao (PHJCC)." Although studies have been conducted to characterize the therapeutic activities of these different plant species, their antioxidant activity has never been investigated. In this study, our aim was to evaluate the antioxidant and free radical scavenging activities of these three different plant materials. At a concentration of 10 mg/ml, results showed that HD possesses the strongest inhibition on the FeCl2-ascorbic acid induced lipid peroxidation in rat liver homogenate, followed by HC and MP. MP showed a weak anti-lipid peroxidation activity at 1 and 3 mg/ml. Using Electron Spin Resonance (ESR) analysis, the order of superoxide anion scavenging activity was HC > HD > MP. However, MP was found to have the greatest hydroxyl radical scavenging activity compared to HC and HD. In conclusion, all three species used as PHJCC in Taiwan exhibited different antioxidant and free radical scavenging activities; these differences could explain, at least in part, the variation in therapeutic properties of PHJCC products in the market.