The methanolic extract of the root wood of Michelia compressa (Maxim.) Sargent showed cytotoxicity against MCF-7, NCI-H460 and SF-268 cancer cell fines. Bioassay-guided fractionation of the chloroform-soluble layer led to the isolation of costunolide and liriodenine with cytotoxic activities, along with the isolation of twenty-seven known compounds. The active costunolide existed as major constituent in this study.