Objective:To investigate the expression of miR-155 in papillary thyroid cancer(PTC) tissue and plasma,and to evaluate the significance of plasma miR-155 level as a biomarker for PTC patients. Methods:Real-time fluorescence quantitative polymerase chain reaction was used to detect the change of miR-155 in tumor tissues and plasma of 52 PTC cases and 32 nodular goiter cases,as well as in plasma of 30 controls. Receiver operating characteristic(ROC) curves were drawn to evaluate the diagnostic threshold as well as the correlation between plasma miR-155 expression and tumorous tissue in PTC patients. Results:The average of miR-155 expression in PTC tumorous tissues and nodular goiter tissues was 8.43 ± 6.14 and 1.14 ± 0.41 respectively. The relative level of miR-155 in plasma of PTC and nodular goiter was 3.35 ± 1.85 and 1.41 ± 0.24,respectively. ROC curves for miR-155 to distinguish PTC and the control group yielded an AUC of 0.932(95%CI:0.851~0.970)(P < 0.001)and nodular goiter yielded an AUC of 0.887 (95%CI:0.811~0.961)(P < 0.001). There was a positive correlation of miR-155 expression between plasma and tumorous tissue in PTC patients (r=0.589,P < 0.000 1). However,there was no relevance between the expression of plasma miR-155 and the clinical characteristics of the study population(P > 0.05). Conclusion:miR-155 expression is upregulated in patients with PTC. Plasma miR-155 may be used as a noninvasive biomarker for the prediction of papillary thyroid cancer.