Abstract: Investigation of the antiproliferative property of Streptocaulon baumii Decne. (Apocynaceae) leaves showed that the hexane fraction nonselectively inhibits cell proliferation of BJ, A549, HCT116 and MCF-7 cell lines using WST-1 cell proliferation assay. In a bioassay- guided scheme, loliolide (1), luteolin 3ʹ-methoxy ether (2) and ursolic acid (3) were isolated. MTT assay indicated that ursolic acid has the highest cytotoxicity against HeLa, MDA-MB231, Cos7 and RAW264.7. The IC50 of the purified compounds against a panel of cell lines is in the low micromolar range. This is the first report on the cytotoxicity of S. baumii against cancer cells as well as the first report of the isolation of the three compounds from plants of the Streptocaulon genus.