Periodontitis is a bacteria-induced disease that always clinically defined as loss of attachment, periodontal pocket and bone loss. Its mechanisms were considered to be complicated, involving an imbalance of the formation and resorption of bone. We sought to determine the function and mechanisms of the effects of B cells on osteoclastogenesis. We purified memory B cells from periodontitis or healthy animals and culture them. Receptor activator of nuclear factor kappa-B ligand (RANKL), expressed by gingival memory B cells, was detected by flow cytometry, enzyme-linked immunosorbent assay and real-time quantitative polymerase chain reaction (RT–qPCR). To discover any direct effects on osteoclastogenesis, gingival memory B cells were co-cultured with bone marrow mononuclear cells, osteoclast number and genes related to osteoclast differentiation were examined. In further investigations, an adoptive transfer experiment of memory B cells was designed, and pathologic indexes and expression of associated cytokines in different tissues were also investigated. We find that memory B cells from inflammatory gingiva produced more RANKL. Notably, such B cells promote osteoclastogenesis. In an adoptive transfer experiment, memory B cells enhanced alveolar bone loss and osteoclast formation. We also find a higher expression of RANKL, TNF-α, IL-1β and IL-17A in gingival crevicular fluid, gingiva and cervical lymph nodes of adoptive transfer group. Our findings highlighted the considerable importance of B cells in alveolar bone homeostasis independent of antibody production during periodontitis.