AIM To investigate the anti-HBV effect ofoxymatrine (oxy) in vivo.METHODS HBV transgenic mice were producedby micro-injection of a 4.2kb fragmentcontaining the complete HBV genomes.Expression level of HBsAg and HBcAg in thetransgenic mice liver was determined byimmunohistochemical assay.RESULTS Four groups (6 mice in each group)were injected intraperitoneally with oxy at thedosage of 100,200, and 300 mg/kg or with salineonce a day for 30 days. Both HBsAg and HBcAgwere positive in livers of all the six mice in thecontrol group (injected with saline), and werepositive in livers of two mice in 100 mg/kg groupand 300mg/kg group. In 200mg/kg group,HBsAg and HBcAg were negative in livers of allthe six mice. Based on the results, 200 mg/kg isthe ideal dosage to explore the effect of oxy atdifferent time points. According to the oxytreatment time, mice were divided into fourgroups: 10 d, 20 d, 30 d and 60 d (4 mice in eachgroup). Each mouse underwent liver biopsy twoweeks before the treatment of oxy. Down-regulation of HBsAg and HBcAg appeared aftertreatment of oxymatrine for 10 d and 20 d, Dane-like particles disappeared after the treatment ofoxy for 20d under electron microscopy,however, the expression level of HBsAg andHBcAg returned to normal 60 d later after oxytreatment.CONCLUSION oxymatrine can reduce thecontents of HBsAg and HBcAg in transgenic miceliver, longer treatment time and larger dosagedo not yield better effects.