Mesenchymal stem cells (MSCs) favor cancer growth by facilitating immunosuppression status in tumor microenvironment. However, the function and mechanism of MSCs in initiating and developing prostate cancer remains to be fully understood. In this study, we first found that MSCs promoted prostate cancer (PCa) tumor growth in vivo and cell proliferation in vitro by using PCs cell strain RM-1. Both exogenous and endogenous MSCs could be recruited into the tumor microenvironment by using bone-marrow transplantation model. We further demonstrated that PDGF-BB produced by RM-1 cell promoted MSCs proliferation in vivo and in vitro, which was abrogated by Si-RNA specific to PDGF-BB. And inflammatory cytokines, such as interferon gamma, tumor necrosis factor alpha, and anti-inflammatory cytokine transformation growth factor alpha, further increased the ability of RM-1 to produce PDGF-BB. Overall, PCa cells produced PDGF-BB favors the proliferation of MSCs, which may elicit immunosuppressive function and enable PCa cells to escape from the immunity surveillance in tumor inflammatory microenvironment. J. Cell. Biochem. 114: 1510–1518, 2013. © 2013 Wiley Periodicals, Inc.