[Background] Plasma cells (PCs) play an important role in humoral immune response that ensures long-term protection against pathogens. Long-lived PCs mostly reside in bone marrow and continue to produce neutralizing antibodies against pathogens for several months to years. However, the mechanism for maintenance and survival of long-lived PCs was not fully understood. Here, we have focused on bone marrow mesenchymal stem cells (MSCs) as a potential niche for the PCs. [Objective] To clarify whether MSCs could contribute as a niche for PCs in terms of their survival and antibody production. [Methods & Results] MSCs and PCs were sort-purified from bone marrow cells of wild type mice by flow cytometer. PCs were co-cultured with MSCs or cultured alone for 7 days. Then, we counted for IgG-producing cells by ELISpot assay. The number of IgG-producing PCs was significantly increased when co-cultured with MSCs. We found that MSCs released IL-6 which supports the PCs survival and Ig secretion. On the other hand, transwell assay indicated that the contact between MSCs and PCs acted on the antibody production inhibitory. We focused on paired Ig-like receptor B (PIR-B) which contains immunoreceptor tyrosine-based inhibitory motif (ITIM), and co-cultured Pirb–/– PCs and wild type MSCs. As a result, IgM concentration, not IgG, was significantly increased in supernatant of Pirb–/– PCs compared with wild type PCs cultured with MSCs. Furthermore, we found that IL-6 production was increased in supernatant of MSCs co-cultured with Pirb–/– PCs than with wild type PCs. [Conclusion] These data showed that MSCs play a role in maintaining PCs. Also, it was suggested that IL-6 production from MSCs was regulated by the signal through PIR-B, and involved in IgM production from PCs.