Potential antioxidant activities of methanol and water extracts of Cirsium japonicum var. ussuriense (CJ) leaves were examined. The reducing power and hydroxyl raical-scavenging activity assays showed that the methanol extract had a significantly higher activity than the water extract. In addition, the methanol extract showed a concentration-dependent reducing power, ranging from 0.228 to 1.072($0.1{sim}0.5;mg/mL$), as well as a high DPPH free radical-scavenging activity($EC_{50}=40.25;{mu}/mL$). The total phenolic(as tannic acid) and flavonoid(as quercetin) contents of the extract were 62.41 mg/g and 13.48 mg/g, respectively. The cytotoxic activity indicated that the methanol extract has an inhibition activity in the stomach carcinoma cell (35.40%), suggesting that the methanol extract of CJ leaves could be used as a potential source of pharmaceutical material.