Chisocarpene A (1) is a new tirucallane-type triterpenoid together with odoratone (2) and 24-methylenecycloartanol (3), isolated from the stem bark of Chisocheton lasiocarpus. The chemical structures of compounds 1-3 were elucidated through a detailed analysis of their spectroscopic data (IR, MS, 1 D, and 2 D NMR). The isolated compounds were evaluated for cytotoxic activity against the MCF-7 breast cancer cell line using a resazurin-based assay. Compound 1 showed the most potent activity (IC50 26.56 ± 1.01 µM) and was two-fold more active than the positive control.