Ovarian cancer is the leading cause of gynecologic cancer deaths among women. Although platinum-based chemotherapy is the first-line treatment for human ovarian cancer, chemoresistance remains a major obstacle to successful treatment, and there are currently no approved molecularly targeted therapies. Recent evidence indicates that signal transducer and activator of transcription-3 (STAT3) is a determinant of chemoresistance and is related to tumor recurrence in a large number of solid malignancies. In this study, we demonstrated that high levels of pSTAT3 were associated with chemoresistance in human ovarian cancer cells. Targeting STAT3 by siRNA technology markedly enhanced cisplatin-induced apoptosis in cisplatin-resistant ovarian cancer cells that expressed a high level of pSTAT3. Interleukin-6 (IL-6) could induce STAT3 activation in cisplatin-sensitive ovarian cancer cells and led to protection against cisplatin. The STAT3 siRNA treatment also blocked IL-6-induced STAT3 phosphorylation, resulting in the attenuation of the anti-apoptotic activity of IL-6. We found that the combination of cisplatin and STAT3, siRNA resulted in the collapse of the mitochondrial membrane potential, attenuated the expression of Bcl-xL and Bcl-2, and increased the release of cytochrome C and expression of Bax. Taken together, these results suggest that the pharmacological inhibition of STAT3 may be a promising therapeutic strategy for the management of chemoresistance in ovarian cancer. (c) 2013 Elsevier Inc. All rights reserved.