A B cell-specific growth substance (BGS) was isolated from the slime layer of Bacillus licheniformis E1. Unlike LPS, the BGS was not affected by polymixin B, an inhibitor of LPS, or by TLR4, and resulted in the growth of B cells. When BALB/c mice were treated with the BGS, the B cell population was found to increase in both the bone marrow and the spleen, with a marked increase after 24 h in the bone marrow and after 48 h in the spleen. When using antibodies to B cell lineage-restricted surface molecules to analyze the B cell population changes resulting from treatment with the BGS, an increase in immature B cells (IgM+ and AA4.1+) and mature B cells (IgM+ and IgD+) was found in the bone marrow 24 h after treatment with the BGS, whereas a decrease in mature B cells and increase in IgG+ B cells were found in the spleen. When the BGS and OVA antigen were injected into the peritoneal cavity of BALB/c mice, this resulted in a high OVA-specific antibody titer in the sera, similar to that induced by aluminum hydroxide. Therefore, it is anticipated that the mass production of the BGS by B. licheniformis E1 could be used for studies of B cells in immunology, and contribute to the development of a new adjuvant for vaccine manufacture.