A case of primary gastric alveolar soft-part sarcoma is presented. The tumor was found in the gastric remnant of a 67-year-old male who had undergone partial gastrectomy due to hemorrhagic gastric ulcer 13 years before. It was located mostly in the submucosa arising from the muscularis propria. The large eosinophilic cells showed the characteristic alveolar compartmentalization and contained intracytoplasmic periodic acid-Schiff-positive granules and typical crystals. Numerous electron-opaque secretory granules in the tumor cell cytoplasm, in addition to crystals of 9 nm periodicity, were confirmed at the ultrastructural levels. Immunostaining failed to detect muscle-related antigens. In contrast, methionine-enkephalin and neuropeptide Y appeared positive in the tumor cells. Interstitial spindle cells showed an occasional positivity to S-100. This is the first case of such a tumor occurring in the gastrointestinal tract, and the findings suggest that gastric alveolar soft-part sarcomas may have a different origin from those arising in the skeleton.