Cirsium japonicum is a wild perennial herb that has been used as an anti-hemorrhagic, anti-hypertensive and uretic agent in traditional Chinese medicine. Recently, it was reported that C. japonicum inhibits the growth of implanted cancer cells. However, the molecular mechanisms underlying the anti-cancer properties of C. japonicum are not fully understood. In this study, we investigated the effect of a methanol extract of C. japonicum on cell growth in the human breast cancer cell line MCF-7. C. japonicum extract inhibited the cell proliferation of MCF-7 cells in a time- and dose-dependent manner, as evaluated by the MTT assay. Furthermore, C. japonicum extract induced an anti-proliferative effect by causing G1 phase cell cycle arrest and also induced apoptosis by affecting mitochondrial apoptotic events, as determined by nuclear derangement, flow cytometry and Western blot analysis. Taken together, our findings indicate that C. japonicum extract induces the inhibition of MCF-7 cell growth at both the proliferation and apoptosis levels.