: Oral lichen planus (OLP) is a chronic and common disease of the oral mucosa, which its etiology, phathogenesis and exact treatment is not definitely known. T-cell mediated immunity is the most probable factor in pathogenesis of OLP. Since TNF-a primarily, as a cytokine, interfers T-Cel mediated immunopathologic reactions, it may also interfere with pathogenesis of OLP.In an observational case- control study, the values of TNF-a in serum of OLP patients were measured and compared with the values of healthy cases. 30 OLP patients and 30 healthy controls have examined with ELISA technique. Data was obtained by observation questionnaire and examination.The mean value of TNF-a in case and control groups were 26.2 and 7.9 pg/ml, respectively, which showed significant difference (PO.005).Considering the TNF-a values with respect to sex and age did not show any significant difference,however the lower TNF-a value was obtained with increasing the age, and higher value observed in females. Higher values of TNF-a found in OLP patients compared with control group. It means TNF-a is an effective factor in OLP. Due to these findings new treatment protocols have been suggested.