Objective To study in vitro anti-HIV activity of an extract of herb medicines,SanJiangDan,and the possible mechanism.Methods The main active ingredient of SanJiangDan was extracted by distillation.Three subtypes of HIV pseudovirus (B subtype,C subtype,CRF01_AE subtype) were used to evaluate the anti-HIV activity of SanJiangDan extract in vitro.The possible mechanism was evaluated through analyzing the effects of SanJiangDan extract on the expression of surface receptors and cytokines by T cells.The cytotoxicity of SanJiangDan extract was detected by using four different sources of cell lines including epithelial cells Caco-2 cells,TZM cells,Huh7 cells derived from liver cells and lymphocyte Jurkat-T cells.Results SanJiangDan extract effectively inhibited the infection of HIV pseudoviruses at concentrations of 1.6 mg/ml and 0.16 mg/ml.The inhibition rates were 30.9％,36.6％ and 65.0％ for B subtype,C subtype and CRF01_AE subtype respectively at the concentration of 0.16 mg/ml.As the concentration increased to 1.6 mg/ml,the inhibition rates increased to 96.4％ (B subtype),97.4％ (C subtype) and 99.5％ (CRF01_AE subtypes),but no toxicity to host cells was detected.Moreover,SanJiangDan extract inhibited the expression of HIV surface receptors including CD4,CXCR4 and CCR5 on TZM-bl cells,but enhanced IL-2 production.Conclusion SanJiangDan extract could inhibit HIV pseudovirus infection without causing cytotoxicity to host cells in vitro.The possible mechanism might be associated with the reduced expression of CD4,CXCR4 and CCR5 and enhanced secretion of IL-2 as well.