This study aimed to investigate whether the crosstalk between the osteoprotegerin (OPG)/receptor activator of nuclear factor-kB (RANK)/receptor activator of nuclear factor-kB ligand (RANKL) in bone marrow mesenchymal stem cells (BMSCs) and Wnt/b-catenin pathways in Pca cells regulates bone metastasis of PCa. Our study showed that there was increased OPG/RANKL/RANK and b-catenin expression in the tissue of PCa and its bone metastasis. This study further showed that RANKL knockdown in BMSCs or b-catenin knockdown in PC-3s blocked the proliferation and migration of BMSCs and the proliferation, migration, and invasion of PC-3s in vitro. Conversely, RANKL overexpression in BMSCs and b-catenin overexpression in PC-3s promoted the proliferation and migration of BMSCs and the proliferation, migration, and invasion of PC-3s in vitro. These data indicate that the RANKL pathway in BMSCs promoted the PC-3s invasion and the catenin pathway in PC-3s activated BMSCs with expression of cancer-associated fibroblast markers, which promoted the bone metastasis. This suggests that the interaction and crosstalk between BMSCs in bone microenvironment and PCa play a critical role in the exquisite tropism for Pca bone metastasis. Cancer therapies classically target tumour cells; however, based on this study, targeting BMSCs in bone microenvironment is a reasonable option for PCa therapy strategy.