Berberine (BBR) is an isoquinoline alkaloid extracted from medicinal plants such as Hydrastis canadensis, Berberis aristata and Coptis chinensis. BBR displays a number of beneficial roles in the treatment of various types of cancers, yet the precise mechanisms of its action remain unclear. Cisplatin is an effective cancer chemotherapeutic agent and functions by generating DNA damage, promoting DNA damage-induced cell cycle arrest and apoptosis; however, its efficacy is challenged by the resistance of tumor cells in clinical application. The aim of the present study was to investigate the effects of BBR in combination with cisplatin on human breast cancer cells. MTT assay showed that BBR inhibited breast cancer MCF-7 cell growth with a 50% inhibitory concentration (IC50) value of 52.178±1.593 µM and the IC50 value of cisplatin was 49.541±1.618 µM, while in combination with 26 µM BBR, the IC50 value of cisplatin was 5.759±0.76 µM. BBR sensitized the MCF-7 cells to cisplatin in a time- and dose-dependent manner. After treatment of BBR and cisplatin, the cellular pro-apoptotic capase-3 and cleaved capspase-3 and caspase-9 were upregulated and the anti-apoptotic Bcl-2 was downregulated. Importantly, BBR restrained the expression of cellular PCNA, and immunofluoresence analysis of γH2AX showed that BBR increased the DNA damages induced by cisplatin. Taken together, the results demonstrated that BBR sensitized MCF-7 cells to cisplatin through induction of DNA breaks and caspase-3-dependent apoptosis.