The tripartite motif protein 38 (TRIM38), a member of the TRIM family, is involved in various cellular processes such as cell proliferation, differentiation, apoptosis, and antiviral defense. However, the role of TRIM38 in osteoclast and osteoblast differentiation is not yet known. In this study, we report the involvement of TRIM38 in osteoclast and osteoblast differentiation. Overexpression of TRIM38, in osteoclast precursor cells, attenuated receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast formation, RANKL-triggered NF-κB activation, and expression of osteoclast marker genes, such as NFATc1, osteoclast-associated receptor (OSCAR), and tartrate-resistant acid phosphatase (TRAP); and down-regulation of TRIM38 expression showed the opposite effects. Ectopic expression of TRIM38 in osteoblast precursors induced increased osteoblast differentiation and function. Elevated expression of alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin was also observed due to blockade of NF-κB activation. Conversely, knockdown of TRIM38 showed the opposite effects. TRIM38 also induced degradation of lysosome-dependent transforming growth factor beta-activated kinase 1 and MAP3K7-binding protein 2 (TAB2), further blocking NF-κB activation. Taken together, our data suggest that TRIM38 plays a critical role in bone remodeling as a negative regulator of NF-κB in both osteoclast and osteoblast differentiation.