Interleukin-6(IL-6) stimulate osteoclast differentiation. 17β-estradiol, 1,25-dihydroxyvitamin D₃(1,25-(OH)₂D₃) and interleukin-1β 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 17β-estradiol and 1,25(OH)2D3 on IL-6 production of PDL cells, PDL cells were treated with 17β-estradiol or 1,25-(OH)₂D₃ in the absence or the presence of IL-1β. 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-1β increased IL-6 synthesis at 1st day and 2nd day. 17β-estradiol had no significant effect on the secretion of this cytokine, either constitutively or after stimulation with IL-1β(0.05 ng/ml). 1,25-(OH)₂D₃(10^-8M) decreased not only constitutive IL-6 production but also IL-1β-induced IL-6 production at 2nd day. These results suggest that 1,25-(OH)₂D₃ may control IL-1beta-induced osteoclast differentiation by decreasing IL-1β-induced IL-6 secretion of PDL cells.