Interleukin-6(IL-6) stimulate osteoclast differentiation. $17{eta}$-estradiol, 1,25-dihydroxyvitamin $D_3$(1,25-$(OH)_2D_3$) and interleukin-$1{eta}$ inhibit or stimulate osteoclast differentiation by decreasing or increasing the synthesis of interleukin-6(IL-6) from stromal/osteoblastic cells, respectively. Periodontal ligament(PDL) cells reside between the alveolar bone and the cementum and have osteoblastic characteristics. To estimate the effect of $17{eta}$-estradiol and 1,25$(OH)_2D_3$ on IL-6 production of PDL cells, PDL cells were treated with $17{eta}$-estradiol or 1,25-$(OH)_2D_3$ in the absence or the presence of IL-$1{eta}$. The concentration of IL-6 produced form PDL cells was determined by enzym linked immunosorbent assay(ELISA). In unstimulated PDL cells, we detected constitutive production of IL-6 at 1st and 2nd day. IL-$1{eta}$ increased IL-6 synthesis at 1st day and 2nd day. $17{eta}$-estradiol had no significant effect on the secretion of this cytokine, either constitutively or after stimulation with IL- $1{eta}$(0.05 ng/ml). 1,25-$(OH)_2D_3$($10^{-8}M$) decreased not only constitutive IL-6 production but also IL-$1{eta}$-induced IL-6 production at 2nd day. These results suggest that 1,25-$(OH)_2D_3$ may control IL-$1{eta}$-induced osteoclast differentiation by decreasing IL-$1{eta}$-induced IL-6 secretion of PDL cells.