Examination of the EtOH extract of the Malayan Alstonia penangiana resulted in the isolation of 10 new alkaloids, comprising two ajmaline (1, 2), four macroline oxindole (3-6), and four macroline-akuammiline bisindole alkaloids (7-10). The structures of these alkaloids were determined based on analysis of the spectroscopic data and, in the case of the oxindole 6 and the bisindole alkaloid 7, also confirmed by X-ray diffraction analysis. The bisindole alkaloids 7 and 8 showed pronounced in vitro growth inhibitory activity against an array of human cancer cell lines, including KB, vincristine-resistant KB, PC-3, LNCaP, MCF7, MDA-MB-231, HT-29, HCT 116, and A549 cells with IC50 values in the 0.3-8.3 μM range.