(−)-Epicatechin is a phenolic compound with antioxidant activity that is present in natural food and drinks, such as cocoa and red wine. Evidence suggests that (−)-epicatechin exhibits anticancer activity; however, its mechanism of action is poorly understood. Here, we investigated the anticancer effects of (−)-epicatechin and its mechanism of action in breast cancer cells. We assessed the anticancer activity by cell proliferation assays, apoptosis by DNA fragmentation and flow cytometry. The expression of proteins associated with apoptosis was analyzed by the human apoptosis array. MitoSOXTM Red and biomarkers of oxidative damage were used to measure the effect of (−)-epicatechin on mitochondrial reactive oxygen species (ROS) and cellular damage, respectively. (−)-Epicatechin treatment caused a decreasing in the viability of MDA-MB-231 and MCF-7 cells. This cell death was associated with DNA fragmentation and an apoptotic proteomic profile. Further, (−)-epicatechin in MDA-MB-231 cells upregulated death receptor (DR4/DR5), increased the ROS production, and modulated pro-apoptotic proteins. In MCF-7 cells, (−)-epicatechin did not involve death receptor; however, an increase in ROS and the upregulation of pro-apoptotic proteins (Bad and Bax) were observed. These changes were associated with the apoptosis activation through the intrinsic pathway. In conclusion, this study shows that (−)-epicatechin has anticancer activity in breast cancer cells and provides novel insight into the molecular mechanism of (−)-epicatechin to induce apoptosis.