Abstract： Objective To investigate the expression and clinical significance of miRNA-155 and miRNA-146a in peripheral blood mononuclear cells(PBMC) and plasma of oral lichen planus(OLP) patients.Methods Twenty-five female and seven male OLP patients(OLP group) aged 25 to 54 years were selected from January 2012 to May 2013.The diagnosis was confirmed by pathology and the lesions were divided into two non-erosive OLP group(18 cases) and erosive OLP group(14 cases).Twenty healthy sex and age matched volunteers served as control,miRNA-155 and miRNA-146a expressions in PBMC and plasma were examined by real-time PCR.The difference between OLP group and control group was statistically analyzed.Results The expressions of PBMC and plasma miRNA-155 were higher in OLP patients than those in the healthy control (median,0.07 vs 0.03,P＜0.05; 5.84 vs 1.32,P＜0.01).The median expression level of miRNA-146a in PBMC and plasma of OLP patients and healthy controls were (1.26 vs 0.58,P＜0.05) and (412.60 vs 238.42,P＜0.01).The plasma miRNA-155 and miRNA-146a expressions were significantly higher in erosive OLP group than those in non-erosive OLP group.There were no significant differences in the expression of PBMC miRNA-155 and miRNA-146a between the two groups.Conclusions The expressions of PBMC and plasma miRNA-155 and miRNA-146a are higher in OLP patients.The expressions of plasma miRNA-155 and miRNA-146a are associated with OLP severity.The over expression of miRNA-155 and miRNA-146a in OLP may play a role in the pathogenesis of OLP.