Background: The survival of stem cells upon transplantation into ischemic myocardium is a major concern in cell-based therapy. In this study, we tested the hypothesis that activation of opioid receptors would enhance the survival of mesenchymal stem cells (MSCs) upon exposure to an injury stimulus. Methods and Results: MSCs were obtained from rat bone marrow and cultured in basal DMEM cell culture medium. Delta-opioid receptor (DOR) was present in MSCs as examined by reverse transcription-polymerase chain reaction and immunochemistry. Activation of DOR with 5μmol/L SNC80 (DOR agonist) for 24h significantly enhanced MSC viability upon exposure to 5μg/ml actinomycin D as determined by TUNEL and MTT assays. The cytoprotection was abolished with 20μmol/L naltrindole hydrochloride (a DOR antagonist). Treatment of the cells with 1.5μmol/L chelerythrine (protein kinase C inhibitor) and 1.25μmol/L WP1066 (signal transducer and activator of transcription 3 (STAT3) inhibitor) blocked SNC80-induced cytoprotection. Furthermore, treatment of the cells with chelerythrine also blocked STAT3-phosphorylation and Mcl-1 gene expression. Conclusions: Taken together, the results indicate that DOR plays a critical role in MSC survival upon exposure to actinomycin D through activation of protein kinase C and its downstream signaling molecules STAT3 and Mcl-1. DOR may be a novel therapeutic target for stem cell survival during cell-based therapy. (Circ J 2012; 76: 204-212)