Abstract： Objective To evaluate the value of imaging studies in diagnosis and differentiating malignant from benign main duct intraductal papillary mucinous neoplasms (MD-IPMNs).Methods The imaging studies of a total of 31 patients with MD-IPMNs confirmed by pathology after surgery was retrospectively reviewed.All patients underwent either CT,MR or MRCP.Two radiologists observed the lesions' imaging feature,and then the lesions was scored,and the differentiation between malignant and benign was made.The Bland Altman method was used for evaluation of inter-observer agreement.The score of the lesions was compared with the pathological results.Finally,a ROC curve was used to calculate AUC,and to evaluate the role of the maximum diameter of the main pancreatic duct (MPD) obtained by imaging studies in differentiation of malignant and benign IPMNs,and to determine the best cut-off point,and sensitivity,specificity.Results Histological analysis revealed low grade dysplasia in 13 patients,middle grade dysplasia in 6 and high grade dysplasia in 5,and adenocarcinoma in 7.Imaging studies suggested benign lesions in 16,malignant lesions in 10 patients and disdiagnosis in 5.The inter-observer agreement on major imaging features was good.The maximum diameter of the MPD was clinically meaningful for distinguishing malignant from benign lesions,and the AUC was 83.8％,and the best cut-off value was 14.8 mm,the sensitivity and specificity was 66.7％ and 100％.The presence of wall nodules could be an imaging feature for distinguishing malignant from benign lesions,but the size of nodules,location of nodules within pancreatic duct,the atrophy of pancreatic parenchyma,and dilated bile duct was not useful for differentiation.Conclusions The imaging studies are sensitive for diagnosis and differentiation between malignant and benign MD-IPMNs,and it is of clinical value for preoperative diagnosis and follow up.