Smooth muscle tumors of stomach are unusual tumors, accounting for 1-3% of primary gastric malignancies. Diagnosis of these tumors is important because of the more favorable prognosis of this tumor than that of gastric carcinoma. A retrospective study was made in 18 patients who had pathology-proven gastric leiomyoma and leiomyosarcoma to identify radiologic characteristics for recent 6 years from Jan. 1978 to July. 1984 at department of radiology, Seoul National University Hospital. The results were as follows: 1. Age of 13 cases of gastric leiomyosarcoma ranged from 36 to 70 with average of 51 and the male to female raio was 10:3. Age of 5 cases of gastric leiomyoma ranged from 24 to 67 with average of 44 and the male to female raio was 3:2. 2. Clinically, gastric leiomyosarcoma had epigastric pain in 7 cases, palpable mass in 4 cases, melena in 3 cases, hematemesis in 2 cases, 5 cases of gastric leiomyoma also had above symptoms respectively. 3. Of the 13 cases of gastric l iomyosarcoma studied by upper gastrointestinal examination, 6 cases(32%) involved the fundus, 10 cases(50%) in the body, 4.. The size of the 13 gastric leiomyosarcomas ranged from 5 to more than 20cm in diameter. The size of the 5 gastric leiomyomas ranged from 3 to 9cm in diameter. 5. The growth type of gastric leiomyosarcoma was exophytic in 8 cases, endogastric in 1 case and mixed pattern in 4 cases. The growth type of gastric leiomyoma were exophytic in 1 case, endogastric in 2 cases and mixed in 2 cases. 6. Mucosal pattern of gastric leiomyosarcoma were mainly effaced pattren in 10 cases(77%), but 3 cases(23%) showed irregular destruction. 1 case of gastric leiomyoma showed mucosal irregularity. 7. Ulceration was present in 10 cases of gastric leiomyosarcoma either single or multiple. 2 cases of gastric leiomyoma showed small ulcerations. Calcifiation was seen in one case of cellular leiomyoma. 8. Diagnostic accuracy of gastric leiomyosarcoma and gastric leiomyoma by U.G.I. stud was 90% and 80% respectively. One case of gastric leiomyosarcoma arose from the fundus of stomach was diffcult to difficultiate from advanced atomach cancer, Borrmann type 1.