Dual immunoglobulin (Ig) domain‐containing adhesion molecule (DICAM) is involved in cell–cell adhesion through a heterophilic interaction with αVβ3 integrin, which suggests that DICAM may participate in osteoclast differentiation. DICAM was localized in the plasma membrane of RAW264.7 and THP‐1 cells, and its expression gradually increased during osteoclastogenesis in mouse bone marrow‐derived macrophages (BMMs) treated with receptor activator of nuclear factor κ‐B ligand (RANKL) and macrophage colony‐stimulating factor (M‐CSF). Forced expression of DICAM in BMMs and RAW264.7 cells blocked the generation of tartrate‐resistant acid phosphatase (TRAP)‐positive osteoclasts. Conversely, knockdown of DICAM by small hairpin RNA (shRNA) increased osteoclast formation in RAW264.7 cells. DICAM‐mediated suppression of osteoclast differentiation was in part due to the inhibition of the p38 mitogen‐activated protein (MAP) kinase pathway, which was corroborated by a decrease in the expression of c‐Fos and nuclear factor of activated T cells (NFAT)c1. Mechanistically, DICAM directly interacted with integrin β3, which inhibited heterodimerization between integrin αV and β3. Exogenous expression of integrin β3 or high‐dose M‐CSF rescued DICAM‐mediated inhibition of osteoclastogenesis, suggesting crosstalk between the integrin β3 and c‐Fms pathways. Finally, recombinant DICAM ectodomain suppressed the RANKL‐ and M‐CSF–induced osteoclastogenesis of BMMs. Collectively, these results indicate that DICAM acts as a negative regulator of osteoclast differentiation by suppressing the integrin αVβ3 pathway. © 2012 American Society for Bone and Mineral Research.