Two rare cases of gastric leiomyoma with cyst formation are reported. Case 1: 74-year-old man visited the hospital because of an abdominal tumor. On admission an irregular surface mass (12×12 cm) was palpable at the epigastric region. Gastrofiberscopy and abdominal computed tomography revealed a submucosal tumor with multiple cyst formation. In May 1986, gastrectomy was performed and histological diagnosis was gastric leiomyoma. Case 2: A 60-year-old woman was hospitalized because of nausea and vomiting. Gastrofiberscopy, abdominal CT and ultrasonography revealed a submucosal tumor with cyst formation. In June 1990 partial gastrectomy including the tumor was performed. The histological diagnosis was gastric leiomyoma. Only one case of gastric leiomyoma with cyst formation has been in the Japanese literature. Because of a malignant potential, we should take surgical operation for the first choice.