Background: Poncirus trifoliataRafin. is a traditional medicine with known anti-inflammatory and anti-cancer properties. Traditionally, it is used to control chronic inflammation, allergy and gastrointestinal diseases such as digestive ulcers gastritis in China, Japan, and Korea. Objectives: To evaluate the apoptosis-inducing activity of a P. trifoliatamethanol extract (MEPT) and elucidate the molecular mechanisms. Materials and Methods: The anti-cancer effect of MEPT and its underlying mechanisms were investigated in breast cancer cells using 3,4,5-dimethyl N-methylthiazol-2-yl-2, 5-d-phenyl tetrazolium bromide assay, cell cycle analysis, and western blotting. Results: MEPT suppressed the proliferation of MDA-MB-231 cells with inhibition dose 50% value of 119.44 μg/mL at 24 h, which have features typical of triple-negative breast cancer cells. MEPT also altered the characteristic features of the MDA-MB-231 cells and increased the proportion of cells undergoing sub-G1 arrest. In addition, MEPT increased levels of caspase 8 and 3 in MDA-MB-231 cells, whereas caspase 9 was not detected. In addition, MEPT-induced tumor necrosis factor receptor (TNFR) and TNFR type 1-associated death domain (TRADD) protein and the activations of c-Jun NH(2)-terminal kinase (JNK) and extracellular signal-regulated kinases (ERK). Conclusion: Our results indicate that MEPT has chemotherapeutic potential in triple-negative breast cancer and that at the molecular level its effects are derived from the activations of TNFR and of the mitogen-activated protein kinase pathway.