Two new tetracyclic triterpenes, cucurbitacins Ⅱ_a and Ⅱ_b,found to show significant antibacterial activity, were isolated from the root of Hemsleya amabilis Diels (Cucurbitaceae).Their structures were deduced from their chemical transformadons, IRNMR and mass spectroscopy,the stereochemistry of ring-A hydroxyl groups was confirmed by conversion of Ⅱ_a to a known compound (Ⅲ).Thus Ⅱ_a is the CaⅡ_25- acetyl derivative of dihydrocucurbitacin F and Ⅱ_b, dihydrocucurbitacin F.