The cytokines released by osteoblasts induce bone resorption via the differentiation of osteoclast precursors. In this process, $interleukin-1{eta}$($IL-1{eta}$)-induced bone resorption is mediated by granulocyte macrophage-colony stimulation factor(GM-CSF), interleukin-6 (IL-6), and tumor necrosis factor ${alpha}$($TNF-{alpha}$) released from osteoblasts. Since these cytokines (GM-CSF, IL-6, $TNF-{alpha}$) are produced by not only osteoblasts but also monocytes, and interleukin-10(I1-10) inhibits the secretion of these cytokines from monocytes, it may be speculated that IL 10 could modulate the production of GM-CSF, IL-6, and $TNF-{alpha}$ by osteoblasts, then control $IL-1{eta}-induced$ bone resorption. Therefore, the aims of the present study were to examine the effects of IL-10 on bone resorption. The sixten or seventeen-day pregnant ICR mice were injected with $^{45}Ca$ and sacrificed one day after injection. Then fetal mouse calvaria prelabeled with $^{45}Ca$ were dissected out. In order to confirm the degree of bone resorption, mouse calvaria were treated with Lipopolysaccharide(LPS), $TNF-{alpha}$, $IL-1{alpha}$, IL-8, $IL-1{eta}$, and $IL-1{alpha}$, Then, IL-10 and $interferon-{gamma}$ ($IFN-{gamma}$) were added to calvarial medium, in an attempt to evaluate the effect of $IL-1{eta}-induced$ bone resorption. In addition, osteoclasts formation in bone marrow cell cultures, and the concentration of IL-6, $TNF-{alpha}$, and GM-CSF produced from mouse calvarial cells were investigated in response to $IL-1{eta}$ alone and simultaneously adding f $IL-1{eta}$ and IL-10. The degree of bone resorption was expressed as the ratio of $^{45}Ca$ release(the treated/the control). The osteoclasts in bone marrow cultures were indentified by tartrate resistant acid phosphatase(TRAP) stain and the concentration of the cytokines was quantified using enzyme linked immunosorbent method. As results of these studies, bone resorption was induced by LPS(1 ng/ml ; the ratio of $^{45}Ca$ release, $1.14{pm}0.07$). Also $IL-1{eta}$(1 ng/ml), $IL-1{alpha}$(1 ng/ml), and $TNF-{alpha}$(1 ng/ml) resulted in bone resorption(the rations of $^{45}Ca$ release, $1.61{pm}0.26$, $1.77{pm}0.03$, $1.20{pm}0.15$ respectively), but IL-8 did not(the ratio of $^{45}Ca$ release, $0.93{pm}0.21$). The ratios of $^{45}Ca$ release in response to IL-10(400 ng/ml) and $IFN-{gamma}$(100 ng/ml) were $1.24{pm}0.12$ and $1.08{pm}0.04$ respectively, hence these cytokines inhibited $IL-1{eta}$(1 ng/ml)-induced bone resorption(the ratio of $^{45}Ca$ release $1.65{pm}0.24$). While $IL-1{eta}$(1 ng/ml) increased the number of TRAP positive multinulcleated cells in bone marrow cultures($20{pm}11$), simultaneously adding $IL-1{eta}$(1 ng/ml) and IL-10(400 ng/ml) decreased the number of these cells($2{pm}2$). Nevertheless, IL-10(400 ng/ml) did not affect the IL-6, GM-CSF, and $TNF-{alpha}$ secretion from $IL-1{eta}$(1 ng/ml)-activated mouse calvarial cells. From the above results, it may be suggested that IL-10 inhibites $IL-1{eta}-induced$ osteoclast differntiation and bone resorption. However, the inhibitory effect of IL-10 on the osteoclast formation seems to be mediated not by the reduction of IL-6, GM-CSF, and $TNF-{alpha}$ production, but by other mechanisms.