Macranthoside B (MB) is a hederagenin saponin extracted from the flower bud of Lonicera macranthoides. In this study, we defined the anticancer effect of MB both in vitro and in vivo using cell proliferation assays and xenograft tumor growth assays. Our data indicate that MB inhibits the proliferation of various kinds of cancer cells with IC(50) values in the range of 10-20 microM. Moreover, the volume and weight of xenograft tumors in nude mice treated with 5mg/kgMB were decreased remarkably compared to those of the vehicle control group. Furthermore, DAPI staining and flow cytometry analysis with Annexin V/PI double staining revealed that more apoptotic cells were observed following MB treatment. In addition, degradation of PARP (poly-ADP-ribose polymerase), and activation of the caspase cascade for intrinsic pathways were observed. We also found that the expression of Bcl-2 protein decreased and the protein level of Bax increased which leading to an increase of the Bax/Bcl-2 ratio. Our results showed that MB exhibited strong anti-tumor effect and mitochondrion-mediated apoptosis induction involved in it.