This study investigated the inhibitory capacity of oxymatrine on in vitro hepatitis B virus (HBV) replication. HepG2.2.15 cells were treated with oxymatrine 50, 100, 200, 400, 800 or 1000 mg/l, or with human interferon-alpha2b (IFN-alpha2b 1000 U/l) as a positive control. Levels of hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg) and HBV-DNA in cell supernatants were determined by enzyme-linked immunosorbent assay and fluorescent quantitative-polymerase chain reaction, respectively. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometric analysis and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labelling were used to evaluate the cytotoxicity of oxymatrine. The inhibitory effects of oxymatrine gradually increased as the concentration increased from 200 to 1000 mg/l for HBsAg and HBeAg, and from 200 to 400 mg/l for HBV-DNA. There was no inhibitory effect of oxymatrine at concentrations < 200 mg/l. No significant difference was seen between human IFN-alpha2b (positive control) and oxymatrine >or= 200 mg/l. It is concluded that oxymatrine can inhibit in vitro HBV replication and antigen expression at concentrations >or= 200 mg/l.