Abstract: The level of bone resorptive cytokin, tumor necrosis factor α （TNF α） was assessed in the tissue reseted sites of periodontal disease. As determined by ELISA of tissue extracts,TNFα was detected in all diseased sites. The level of TNFα was significantly higher in the diseased than that of the clinically healthy gingival tissue（t=3.293, P＜0.01）. The result of this study indicates that TNFα is likely to be an important mediator in the pathogenesis of periodontal disease.