Although the ultrasonography & CT have been regarded as a primary procedure in the differential diagnosis of upper abdominal mass, the CT was more superior in the diagnosis, its extent and relationship to the bowel in the cases of the leiomyosarcoma & leiomyoma of the stomach than those of the ultrasonography. The authors studied CT findings of 9 cases of pathologically proven gastric smooth muscle tumor(leiomyosarcoma 7, leiomyoma 2) during the last two years. The results were as follows: 1. CT findings of gastric leiomyosarcoma were often quite large mass, average 15 cm in diameter; extensive central necrotic or cystic changes were found in all 7 cases, seen more clearly on postcontract scan; calcification and peripheral rim enhancement of the tumor were seen in one case each other. 2. Metastasis to the liver and the spleen was seen only in one case, which revealed centrally necrotic and ascites was found in one case. 3. Two cases of gastric leiomyoma were smaller in size, a erage 6.3 cm in diameter than those of leiomyosarcoma ;central necrotic or cystic changes were less common and less extensive. 4. If there were no evidence of central necrotic or cystic changes in large peri-or juxtagastric tumor, ohe should consider other diagnostic possibilities such as left lobe hepatoma, exophytic stomach canceer, lymphoma or other mesenchymal tumors than leiomyosarcoma.