Iron oxide nanoparticles (IONPs) have been widely used as contrast agents for magnetic resonance imaging (MRI) and other biomedical applications in both clinical and preclinical cases. In the present study, we show that two clinically used IONPs, ferumoxytol and ferucarbotran, have an intrinsic inhibitory effect on receptor activator NF-κB ligand (RANKL)-induced osteoclastogenesis of bone marrow-derived monocytes/macrophages (BMMs). IONPs significantly inhibited the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinuclear osteoclasts and functional actin ring structures. More importantly, the inhibitory effect was also verified in vivo by its capacity to rescue the bone loss of ovariectomized (OVX) mice after intravenous injection with IONPs. Mechanistically, we found that IONPs trigger the upregulation of p62 which result in recruitment of CYLD and enhanced deubiquitination of TRAF6, a master controller of RANKL signaling. The downstream activation of NF-κB and MAPK signals was accordingly attenuated, ultimately leading to reduced expression of osteoclatogenesis-related genes. Taken together, clinically used IONPs can inhibit osteoclastogenesis through regulating TRAF6-p62-CYLD signaling complex, and they may be considered as alternative options for treatment of osteoporosis. STATEMENT OF SIGNIFICANCE: Nanoparticles have been developed as drug delivery systems for treatment of osteoporosis, mostly an age-related health problem with risk of fractures. In this work, we show that two clinically used iron oxide nanoparticles (IONPs) ferumoxytol and ferucarbotran themselves can significantly reduce the osteoporosis of ovariectomized (OVX) mice through inhibiting Osteoclastogenesis. We found that IONPs trigger the upregulation of p62 which result in recruitment of CYLD and enhanced deubiquitination of TRAF6, a master controller of RANKL signaling. The downstream activation of NF-κB and MAPK signals was accordingly attenuated, leading to reduced expression of osteoclatogenesis-related genes. Taken together, clinically used IONPs inhibit osteoclastogenesis through regulating TRAF6-p62-CYLD signaling complex, and they may be considered as alternative options for treatment of osteoporosis.