Abstract： Objective To detect the level of plasma miR-155 in patients with pancreatic cancer and evaluate its diagnostic value for pancreatic cancer. Methods Sixty-two cases of pancreatic cancer patients, 61 patients of chronic pancreatitis and 36 normal controls were included in the study. miR-155 in the total RNA extracted from the plasma was measured using real time PCR. The diagnostic parameters and relationship of the miR-155 with clinical characteristics in pancreatic cancer patients were analyzed. Results The relative abundance of plasma miR-155 in pancreatic cancer, chronic pancreatitis and normal controls were 5.41 ±3.14,2.59 ±2.49 and 0.77 ± 1.17, and the value was significantly higher in pancreatic cancer group compared with those of chronic pancreatitis and normal group (P ＜ 0. 01 ). No significant correlation between the level of plasma miR-155 and age, sex, tumor size in pancreatic cancer patients was found. But there was a negative correlation between the level of plasma miR-155 and TNM staging (r = -0. 323, P = 0.01 ). For discriminating pancreatic cancer from normal control, the AUC ROC of miR-155 was 0. 943 (95% CI 0.902-0.985), and the sensitivity and specificity were 87.1% and 83.3%, respectively. For discriminating pancreatic cancer from chronic pancreatitis, the AUC ROC of miR-155 was 0.762 (95% CI0. 678-0. 846),and the sensitivity and specificity were 64.5% and 73.8%, respectively. For discriminating pancreatic cancer from chronic pancreatitis and normal, the AUC-ROC of miR-155 was 0. 829(95% CI0. 767-0.892), and the sensitivity and specificity were 62.9% and 84.5%, respectively. Conclusions Plasma miR-155 was significantly increased in patients with pancreatic cancer, and can be used for diagnosis of pancreatic cancer.