A bioassay-guided fractionation and chemicalinvestigation of the stems of Lagerstroemia indica resultedin the isolation and identification of a new triterpene glycoside,lagerindiside (1), along with nine known triterpenes(2–10). The structure of this new compound was elucidatedon the basis of 1D and 2D nuclear magnetic resonancespectroscopic data analysis as well as chemical method. The cytotoxic activities of the isolates (1–10) were evaluatedby determining their inhibitory effects on four humantumor cell lines (A549, SK-OV-3, SK-MEL-2, andHCT15) using a sulforhodamine B bioassay. Compounds 3and 4 showed potent cytotoxicity on the tumor cell lineswith IC50 values ranging from 3.38 to 6.29 lM.