Objective    To provide exact and reliable morphological data for the operation of endoscopic sphincterotomy (EST).    Method   (1) 20 cadeveric duodenum and pancreas were perfused with latex.  (2)The resource, number, diameter, branches of all carunculae major arteries of these specimens and the distance from vascular origin to Vater bulb, the inner margin of duodenum and carunculae major were observed.         Results   (1) Carunculae major arteries originated from the anterior and posterior arterial arches, and each had two branches. The diameter of the two branches of the anterior carunculae major artery was (1.3±0.1) mm and (1.0±0.2) mm. The distance from the vascular origin of the two branches to the Vater’s ampulla, the inner margin of duodenum and carunculae major was (5.7±0.6) mm and (6.0±0.4) mm, (8.7±1.1) mm and (9.7±1.7) mm, (16±0.9) mm and (16±1.5) mm, respectively. The diameter of the two branches of the posterior carunculae major artery was (0.62±0.02) mm and (0.98±0.06) mm. The distance from the vascular origin of the two branches to Vater’s ampulla, the inner margin of duodenum and carunculae major were (11±0.7) mm and (16.4±0.4) mm ,(13±0.3) mm and (17.9±0.3) mm, (16±0.7) mm and (19.2±0.6) mm, respectively. (2) The first branch of the anterior carunculae major arteries was at the direction 10~11 o'clock and the second branch was at the position 2~3 o'clock. The first branch of the posterior carunculae major arteries was at the position of 8~9 o'clock and the second branch was at the position of 4~5 o'clock. The branches of carunculae major arteries were primarily located at the position of 8~11 o'clock and secondarily at the position of 2~5 o'clock, and least at 11~1 as well as 6~7 o'clock.   Conclusion    In EST the incision should be made at the direction of 11~1 or 6~7 o'clock.