This study is to synthesize sulfated Angelica polysaccharides (APSs) and investigate the activity of one of the sulfated derivatives APS-1 on murine leukemia virus in vivo. Six sulfated derivatives with degree of sulfation ranging from 0.68 to 1.91 were obtained. And the virus replication was inhibited by APS-1 at the dose of 10 and 30 mg/kg (26% and 30% inhibition respectively). Furthermore, both the percentage of CD4(+) cells and CD4(+)/CD8(+) ratio in peripheral blood cells were significantly enhanced by APS-1 at 3-30 mg/kg. In addition, the reduced thymus/body weight index by murine leukemia virus infection was increased by ASP-1 in a dose dependent manner. These results suggest that APS-1 could not only inhibit virus replication, but also improve the immune function. APS-1 may be a potential new and better antiviral drug.