The saponins of Sapindus mukurossi was analyzed by tandem mass spectrometry.The molecular weights of 12 saponins from the total saponin of S.mukurossi were determined by positive and negative ions ESI-MS and their molecular formula were acquired by HR-ESI-MS.Furthermore,the four hederagenin saponins and seven acyclic sesquiterpene saponins were identified based on the tandem mass spectrometry.