The antioxidant property of jionoside D, isolated from Clerodendron trichotomum (Verbenaceae), was investigated. This compound showed scavenging activity of intracellular reactive oxygen species and of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, as well as lipid peroxidation inhibitory activity. This radical scavenging activity of jionoside D protected the cell viability of Chinese hamster lung fibroblast (V79-4) cells exposed H2O2. Furthermore, jionoside D reduced the apoptotic cells induced by H2O2, as demonstrated by the decreased number of sub G1 hypo-diploid cells and apoptotic body formation. However, it increased the activities of cellular antioxidant enzymes, superoxide dismutase and catalase. Taken together, these findings suggest that jionoside D, isolated from C. trichotomum, exhibits antioxidant properties.