Abstract: An aqueous extract of the twigs of Pyrus communis L. var. sativa (DC) DC. showed inhibitory effect against S-180. Compounds were isolated from the twigs of P. communis and eight of them were identified as nonacosane (Ⅰ), lupeol (Ⅲ), β-sitosterol (Ⅳ), betulin (Ⅴ), betulinic acid (Ⅵ), daucosterol (Ⅶ), hydroquinone (Ⅷ) and arbutin (Ⅸ) by MS, NMR, IR, UV and some chemical techniques. It was showed that the compounds Ⅲ, Ⅳ, Ⅴ, Ⅵ, Ⅷ and Ⅸ possessed some bacteriostatic activities on Escherichia coli, Salmonella typhi, Shigclla flexneri and Staphylococus aureus. Primary pharmacology tests showed that Ⅷ had inhibitory effect against S-180 (47.5%).

Key words: Rosaceae, Pyrus communis, pentacyclic triterpenes, phenolic compounds