We report a case of gastrointestinal stromal tumor (GIST) of the pylorus ring which is a rare site. A 71-year-old woman was admitted to the hospital because of anemia detected by a mass screening. We had great difficulty in decision making of tumor location. On CT and magrotic resonance imaging, a movable tumor measuring 6cm seemed to be located in the stomach. But, on endoscopy and gastroduodenography, the tumor was considered to be a submucosal lesion in the duodenum. We perform a laparotomy under a diagnosis of submucosal tumor near the pylorus. A gouse egg sized mass was found and resection of the antrum and duodenal bulb was performed. The resected speciemen showed a solid mass measuring 7.5×5.5cm on the pylorus ring. Pathological examination showed that the tumor was GIST positive for CD34 and c-kit and negative for actin-SM and S-100. GIST on the pylorus ring has not yet been reported so far. This rare case is presented with some bibliographical discussion.