Abstract: Some preparation of the total alkaloids of Ku-Mu (Picrasma quassioides (D. Don) Benn.) was Shown to have antibacterial actiyity in clinical trial. For the exploration of the active principles, the present paper deals with the studies of the alkaloids of this medicinal plant. From an alcohol extract of heartwood of Ku-Mu seven alkaloids were isolated through silica gel and alumina column chromatography as well as preparative thin layer chromatography. Beside the known alkaloids 1-carbomethoxy-β-carboline (Ⅱ), 4,5-dimethoxycanthin-6-one (Ⅳ), canthin-6-one (Ⅴ), and 4-methoxy-5-hydroxycanthin-6-one (Ⅵ), three new alkaloids, named Kumujian A, Kumujian C, and Kumujian C, were ident fied as 1-carboethoxy-β-carbotine (Ⅰ), 1-formyl-β-carboline(Ⅲ) and 1-vinyl-4,8-dimethoxy-β-carboline (Ⅶ), respectively. In virto screening of the above alkaloids demonstrated that 1-carbomethoxy-β-carboline (Ⅱ), 4,5-dimethoxycanthin-6-one (Ⅳ), 4-methoxy-5-hydroxycanthin-6-one (Ⅵ) and 1-vinyl-4,8-dimethoxy-β-carboline (Ⅶ) exhibited inhibition against Staphylococcus aureus and its drug-resistant strains. Tests for the antibacterial activity of three other alkaloids were hampered by scarcity of material.