To investigate the short term anti HBV efficacy of foscarnet sodium, sixty seven patients with various types of chronic hepatitis B were randomly divided into two groups. The experimental group (47 cases) was assigned to receive foscarnet sodium 3 0g by intravenous infusion twice daily in addition to general liver protective medicine for 15 days. The control group (20 cases) was treated with regular liver protective medicine only. The quantity of HBV DNA was measured with equivalent competitive PCR combining with DNA hybridization quantitative detection technique before and after treatment (once a week). The HBV markers and liver functions were also tested before and after treatment. In antiviral therapy group, the patients with different types of hepatitis B had their liver functions improved. HBV DNA in 13 patients became negative by PCR. Two of HBeAg positive patients became sero converted. Foscarnet sodium can inhibit HBV efficiently and quickly. The replication of HBV DNA can be greatly suppressed in the first week but without significant change in the second week in some cases. Foscarnet can be one of the drugs of choice in a combined therapy or as the initial drug in a sequential therapeutic regime.