Abstract: periodontitis patients and 15 health controls are selected to determine the amount of tumor necrosis factor α(TNF α) in inflamed ginival and the normal gingival by RIA. The elations between TNF α and clinical parameters are analysed. The results show that the level of TNF α in inflamed gingival is higher than that in the controls ( P <0.01). The relationship between TNF α and clinical parameters indicate that the level of TNF α positively correlate to the degree of periodontitis and group damagement. It indicates TNF α may be one of the mechanism in the pathogenesis of periodontitis disease.