Study on chemical constituents from the leaves of Kopsia singapurensis (Apocynaceae) yielded a new indole alkaloid, singaporentine A (1) together with two known alkaloids, kopsifoline A (2) and kopsininic acid (3). The structure of 1 was elucidated by combination of various spectroscopic methods such as MS, UV, IR, ID and 2D NMR. Singaporentine A exhibited cytotoxic activity against P388 murine leukemia cells. © 2008 The Japan Institute of Heterocyclic Chemistry.