A novel monoterpenoid indole alkaloid, melognine () possessing an unprecedented skeleton with a 6/6/5/5/6/6 hexatomic rearranged ring system was isolated from the stems of . The structure with absolute configuration of was established by extensive spectroscopic analyses and quantum ECD calculations. Melognine showed significant cytotoxicity on human breast cancer BT549 cells with an IC value of 1.49 μM by MTT assay. Further mechanism of action study indicated that melognine demonstrated the ability to induce apoptosis by activation of caspase-3 and p53, and downregulation of Bcl-2 in BT549 cells.