One new lupane-triterpene glycoside, acankoreoside I (1), and four known compounds, acankoreoside A (2), acankoreoside D (3), acankoreoside F (4), and acantrifoside A (5), were isolated from the leaves of Acanthopanax koreanum (Araliaceae). Their chemical structures were elucidated by mass, 1D- and 2D-NMR spectroscopy. The structure of new compound 1 was determined to be 3alpha,11alpha,30-trihydroxylup-23-al-20(29)-en-28-oic acid 28-O-[alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl] ester. The cytotoxic activities of these compounds were evaluated with four cancer cell lines such as A-549 (lung), HL-60 (acute promyelocytic leukemia), MCF-7 (breast), and U-937 (leukemia). Compound 1 showed growth inhibitory effect in A-549, HL-60, and MCF-7 cell lines with the IC(50) values of 8.2 microM, 12.1 microM, and 28.6 microM, respectively, whereas it was less active in the U937 cell line (the IC(50) >100 microM).