Abstract： Objective　To understand CT features of polypoid ampullary carcinoma by enhanced dual-phase spiral CT.Methods　15 cases of polypoid ampullary carcinoma (PAC) confirmed by surgical and pathological results were studied with thin slice enhanced dual-phase spiral CT (including arterial and portal phase scanning)with retrospective analysis, the scanning parameters were 5 mm thickness and 1.0 pitch for arterial phase scanning , and 5 mm thickness and 5 mm space for portal phase scanning. Results　All cases could display an enhanced mass as local filling defect at the site of the duodenal Vater′s ampulla during arterial and portal phase scanning, the tumors ranged in size from 1 cm to 5 cm with mean of 2.3 cm, all were accompanied with dilated intrahepatic and common bile duct, enlarged gallbladder and dilated pancreatic duct, except one case which had marked atrophy of the pancreatic body and tail. Conclusion　The thin slices enhanced dual-phase spiral CT could not only accurately define the level of obstruction,but also demonstrate an enhanced mass as direct CT sign of the PAC, which is crucial for diagnosis of the PAC.