Bioassay-directed fractionation of an ethanolic extract of the galls of Sapindus mukorossi has resulted in the isolation of two new tirucallane-type triterpenoid saponins, sapinmusaponins Q (1) and R (2), along with three known oleanane-type triterpenoid saponins (3-5). Their structures were elucidated on the basis of spectroscopic analysis and chemical hydrolysis. Biological evaluation showed that both sapinmusaponins Q and R demonstrated more potent anti-platelet aggregation activity than aspirin.