Small molecule BH3 mimetics comprise a promising new chemotherapeutic strategy for treating relapsed or chemoresistant cancer. In this study, we investigated the cellular mechanism of action by which BM-1197, a Bcl-xL/Bcl-2 dual inhibitor, triggers apoptosis in a panel of colorectal cancer (CRC) lines. Using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, we determined that BM-1197 inhibited CRC cell growth in a concentration- and time-dependent manner. The 50 % inhibitory concentration (IC50) values for the most sensitive cell lines, SW620 and SW480, ranged from 0.07 to 1.10 μM in response to a 72-h treatment. In CRC cells, BM-1197 induced apoptotic death without affecting the expression of Bcl-2 family proteins. However, BM-1197 effectively triggered a conformational change in Bax, releasing Bim from Bcl-xL by disrupting the interaction between Bcl-xL and Bak/Bax. Compared with the control group, BM-1197 treatment significantly increased the fraction of SW480 cells in the sub-G1 phase, the apoptosis rate, and cellular internucleosomal DNA fragmentation. The proapoptotic activity was associated with cytochrome c release, caspase-3 activation, and PARP-1 cleavage. Collectively, BM-1197 effectively suppressed the growth of the human CRC cell line SW480 by inducing mitochondria-dependent apoptotic cell death. These data have specific implications for the in vivo analysis and clinical evaluation of BM-1197 in CRC.