Objective: To screen the anti-simian immunodeficiency virus（SIV） active parts of the extracts of stem of Streblus asper.Method: The inhibitory effects of different extracts on SIV were observed when SIV and CEMx174 cell system were employed as the models and azidothymidine selected as the positive control drug.And chemical constituents of the anti-SIV active parts were identified by the test tube method and round filter paper.Result: The results showed that the inhibitory rates of SIV antigen positive cells were 55.9% and 41.2% when 62.5 mg.L-1 of petroleum ether extract and 15.625 mg.L-1 ethyl acetate extract of the stem of S.asper were used.The petroleum ether extract might contain essential oil

grease

steroidal or triterpene material

while the ethyl acetate extract contain phenolic compounds

indicating that the extract had certain inhibitory effect on SIV in vitro

but the other extract of the stem had no such effect.Conclusion: Essential oil

grease

steroidal and triterpene or phenolic compounds in the stem of S.asper may be the substance that has certain inhibitory effects on SIV.