Prostate cancer is the leading type of cancer diagnosed and the third leading cause of cancer-related deaths worldwide each year in men. The limitations of the current prostate cancer screening test demands new biomarkers for early diagnosis of prostate cancer metastasis to bone. In this study, we performed a deep proteomic analysis of secreted proteins from the prostate cancer bone metastasis cell line, PC-3, and normal prostate cell line, RWPE-1. Here, we quantified 917 proteins and found 68 highly secreted in PC-3 versus RWPE-1 cells using LC-MS/MS. To characterize the highly secreted proteins in the PC-3 cell line to identify biomarker proteins, the quantifiable proteins were divided into four quantitative categories (Q1-Q4). The KEGG pathways of lysine degradation and osteoclast differentiation were enriched in Q4, the highly secreted group. Transforming growth factor (TGF) beta family proteins related to osteoclast differentiation were identified as key regulators in PC-3 cells. Among the 68 highly secreted proteins, pentraxin, follistatin, and TGF-beta family members were confirmed by immunoblots. In particular, serpin B3, modulated by TGF-beta, was detected and its selective expression and secretion in PC-3 cells was confirmed. In the present study, we suggest that serpin B3 is a novel biomarker candidate for diagnosis of prostate cancer metastasis to the bone.