Dehydrocorydaline is an alkaloid isolated from traditional Chinese herb Corydalis yanhusuo W.T. Wang. We discovered that it possessed anti-tumor potential during screening of anti-tumor natural products from Chinese medicine. In this study, its anti-tumor potential was investigated with breast cancer line cells MCF-7 in vitro. The anti-proliferative effect of dehydrocorydaline was determined by MTT assay and the mitochondrial membrane potential (ΔΨ m) was monitored by JC-1 staining. DNA fragments were visualized by Hoechst 33342 staining and DNA ladder assay. Apoptotic related protein expressions were measured by Western blotting. Dehydrocorydaline significantly inhibited MCF-7 cell proliferation in a dose- dependent manner, which could be reversed by a caspase-8 inhibitor, Z-IETD-FMK. Dehydrocorydaline increased DNA fragments without affecting ΔΨm. Western blotting assay showed that dehydrocorydaline dose-dependently increased Bax protein expression and decreased Bcl-2 protein expression. Furthermore, dehydrocorydaline induced activation of caspase-7,-8 and the cleavage of PARP without affecting caspase-9. These results showed that dehydrocorydaline inhibits MCF-7 cell proliferation by inducing apoptosis mediated by regulating Bax/Bcl-2, activating caspases as well as cleaving PARP. © 2012 World Scientific Publishing Company & Institute for Advanced Research in Asian Science and Medicine.