To study the level of blood selenium(Se)and nitrogen monoxide(NO)of oral lichen planus patients.Tested the contents of blood selenium(Se)and nitrogen monoxide(NO)of oral lichen planus patients and healthy cases.The level of blood selenium(Se)of oral lichen planus patients was lower than that of the control group,the situation of nitrogen monoxide(NO)was opposite,which indicated that Se and oxyradical may play an important role in the mechanism of oral lichen planus.