Abstract： Objective To increase the awareness of autoimmune pancreatitis (AIP) and correct diagnosis rate of AIP by investigating radiologic characteristic of AIP and small pancreatic cancers.Methods The clinical data and radiologic imaging of 24 AIP patients who met the Asia diagnostic criteria of AIP in 2008 and 25 cases of pathologically condirmed small pancreatic cancer were retrospectively reviewed.All imaging findings were reviewed,especially on the shape,enhancement patterns of mass,pancreatic ducts,peripancreatic and extra-pancreatic manifestations. Chi-square test and Fisher test were used for statistical analysis.Results The imaging signs,including location of masses,distal pancreatic atrophy,enhancing mass during portal phase,truncated duct sign of pancreatic duct,capsule-like rim and renal involvement,was significantly different between AIP and small pancreatic cancer ( x2 =9.010,10.506,15.488,8.688,6.292 and 4.966 respectively,P ＜0.05 ).But only two signs,distal pancreatic atrophy and enhancing mass during arterial and portal phase,were statistically different between local AIP and small pancreatic cancer (P ＜0.05).Conclusions The typical imaging features of diffuse AIP is distinct and helpful for the differential diagnosis of AIP from small pancreatic carcinoma,but there is limited value in the differential diagnosis between local AIP and small pancreatic cancer.