Abstract: Objective: To investigate the effect of Porphyromonas gingivalis(P.g) outer membrane vesicles (OMVs) on bone marrow mesenchymal stem cells (BMSCs) osteogenesis through arginine specific gingipain B (RgpB). Methods: P.g OMVs were isolated and identified, co-cultured with BMSCs. The changes in the gene and protein levels of alkaline phosphatase (ALP), bone morphogenetic protein 2 (BMP2), and osteocalcin (OCN) were detected by real-time fluorescent quantitative PCR (qRT-PCR) and Western blot. To investigate the effect of proteins in P.g OMVs on BMSCs osteogenic differentiation, P.g OMVs were treated with proteinase K to remove their protein components and then co-cultured with BMSCs, and Western blot, ALP staining, and alizarin red staining were used to examine changes in osteogenic ability. The results verified whether P.g OMVs inhibit BMSCs osteogenesis through the proteins they carry. Further, liquid chromatography mass spectrometry analysis of P.g OMVs was conducted to screen for potential protein molecules, RgpB. The effect of RgpB on the osteogenic differentiation ability of BMSCs was verified by qRT-PCR and ALP staining.Results:Both qRT-PCR and Western blot results showed that P.g OMVs inhibited the expression of ALP, BMP2, and OCN genes and proteins in BMSCs. When the protein molecules in P.g OMVs were removed, the expression of ALP and BMP2 proteins in BMSCs increased, along with enhanced ALP activity and mineralized nodule formation. Mass spectrometry analysis revealed high expression of RgpB in the OMVs. When BMSCs were stimulated with RgpB protein, the expression of ALP, BMP2, and OCN genes in BMSCs decreased as RgpB concentration increased (P＜0.05), and ALP activity was suppressed. Conclusion: P.g OMVs can inhibit the osteogenic differentiation of BMSCs by carrying the RgpB.