Abstract: Objective To investigate whether Embelin could synergistically enhance tumor necrosis factor related apoptosis-inducing ligand(TRAIL) -induced apoptotic death in breast cancer cell line MDA-MB-231. Methods Embelin, TRAIL or their combination were applied to treat MDA-MB-231 cells respectively. MTT assay was used to measure the cytotoxicity of drug treatment. APOP-BRUD kit and flow cytometry were used to quantify the apoptosis rate. Western blot was used to observe the activation of Caspase 3, 9 and PARP cleavage. Semi-quantitative RT-PCR and Western blot were used to measure the mRNA and protein expression levels of X-linked inhibitor of apoptosis protein(XIAP) after Embelin treatment. Results Partial MDA-MB-231 cells manifested were resistant to TRAIL. Cytotoxic effect of Embelin on MDA-MB-231 was in a dose-dependent manner. Sub-toxic concentration of Embelin significantly facilitated TRAIL-induced cytotoxicity, apoptosis rates, activation of Caspase 3, 9 and cleavage of PARP. However, sub-toxic concentration of Embelin did not directly alter the protein and mRNA expression levels of XIAP. Conclusion Embelin could significantly enhance TRAIL-induced apoptotic death of MDA-MB-231 cells.