Testosterone has profound immune-modulatory actions, which may be important for the sexual dimorphism in immune-related disorders, such as autoimmune diseases. A well-known effect of androgens is inhibition of bone marrow B lymphopoiesis; however, a plausible target cell for this effect has not yet been presented. The aim of this study was to determine the target cell for androgen-mediated regulation of bone marrow B lymphopoiesis in males. We confirm higher number of bone marrow B cells in male mice with global inactivation of the androgen receptor (AR) and these global AR knockout (G-ARKO) mice had increased number of B cell precursors from the pro-B stage. Because osteoblast-lineage cells are known to support B lymphopoiesis at the pro-B stage, we investigated the effect on B lymphopoiesis in osteoblast-lineage cell-specific ARKO (O-ARKO) mice; O-ARKO mice had increased number of B cells in the bone marrow, and the number of B cell precursors was increased from the pro-B stage, demonstrating that O-ARKO mimics the bone marrow B lymphopoiesis pattern of G-ARKO mice. By contrast, O-ARKO mice displayed only minor changes in B cell numbers in the splenic compartment compared with G-ARKO. Further, O-ARKO mice had moderately reduced number of bone trabeculae in the vertebrae, whereas cortical bone was unaffected. In conclusion, androgens exert inhibitory effects on bone marrow B lymphopoiesis in males by targeting the AR in osteoblast-lineage cells. The identification of the likely target cell for androgen-mediated regulation of bone marrow B lymphopoiesis will contribute to elucidation of the mechanisms by which androgens modulate immune-related disorders.