To study the chemical constituents in rhizome of Pinellia ternata.The constituents were isolated by silica-gel and Sephadex LH-20 chromatography. The structures were identified by spectroscopic analysis including 2D NMR techniques.Six compounds were obtained and identified as stigmast-4-en-3-one(I), cycloartenol(II), 5alpha,8alpha-epidioxyergosta-6,22-dien-3-ol(III), beta-sitosterol-3-O-beta-D-glucoside-6'-eicosanate(IV), alpha-monpalmitin(V), beta-sitosterol(VI). The bioactive assay indicated that: compound III was active against the human tumor cell lines HCT-8, Bel-7402, BGC-823, A549, A2780.Compounds I-IV were isolated from Pinellia ternata for the first time, compound II was the first triterpene isolated from this genus. Compound III may be one of the antitumor constituents of P. ternata.