Abstract： Objective To determine the effect of oxymatrine on the activity of HBV DNA polymerase in vitro. Methods Hepatitis B virus particles were purified from supernatant of cultured HepG2.2.15 cells by uhracentrifugation, and then were mixed with reaction buffer containing NP-40, β-mercaptoethanol, 32P-labelled nucleoside triphosphate (dCTP), MgCl2, and different concentrations of oxymatrine ( 1000 μg/ml, 800 μg/ml, 600 μg/ml, 400 μg/ml and 200 μg/ml) or adefovir dipivoxil ( 100 μg/ml, 80 μg/ml and 60 μg/ml, 40 μg/ml and 20 μg/ml). After incubation at 37 ℃ overnight, proteinase K was added to the reaction system for digestion and 35 μl of samples were spotted onto DE81 paper. Activities of endogenous polymerase in HBV particles were assessed by determining the radioactivity of 32P-labelled dCTP incorporated in the plus-strain of viral DNA. Results Compared with the blank control, the activity of endogenous polymerase in HBV particles treated with different doses of oxymatrine varied from 103% to 107%, and it varied from 91% to 101% when treated with different doses of adefovir dipivoxil. No significant difference was observed among treated groups and the control (P > 0. 05 ). Conclusion No direct inhibitory effect of oxymatrine on the activity of HBV polymerase was observed in vitro.