The betulinic acid (BetA) purified fromPulsatilla chinensis(PC) has been found to have selective inhibitory effects on hepatitis B virus (HBV). In hepatocytes from HBV-transgenic mice, we showed that BetA substantially inhibited HBV replication by downregulation of manganese superoxide dismutase (SOD2) expression, with subsequent reactive oxygen species gen-eration and mitochondrial dysfunction.