Osteoclasts are multinucleated cells that are formed by the fusion of pre-fusion osteoclasts (pOCs). The fusion of pOCs is known to be important for osteoclastic bone resorption. Here, we examined the effect of IFN-${gamma}$ on the fusion of pOCs. IFN-${gamma}$ greatly increased the fusion of pOCs in a dose-dependent manner. Furthermore, IFN-${gamma}$ induced pOC fusion even in hydroxyapatite-coated plates used as a substitute for bone. The resorption area of pOCs stimulated with IFN-${gamma}$ was significantly higher than that of the control cells. IFN-${gamma}$ induced the expression of dendritic cell-specific transmembrane protein (DC-STAMP), which is responsible for the fusion of pOCs. IFN-${gamma}$ enhanced DC-STAMP expression in a dose-dependent manner. The mRNA expression of c-Fos and nuclear factor of activated T cells (NFAT) c1 was enhanced in the pOCs treated with IFN-${gamma}$. Taken together, these results provide a new insight into the novel role of IFN-${gamma}$ on the fusion of pOCs.