Simultaneous a collision tumor of stomach consisting of adenocarcinoma and Gastrointestinal Stromal Tumor (GIST) is very rare based on our knowledge. This coexistence has rarely been reported in literatures. We report a case of 64-year-old woman who has diagnosed with prepyloric poorly-differentiated diffuse signet-ring cell type adenocarcinoma and has undergone an elective D2 total gastrectomy. During operation another mass in fundic body region has found. The pathologic examination of the mass has shown GIST. Immunohistochemical staining for CD117 and Desmin was positive whilst that for S100 was negative. This case reports the simultaneous two tumors development of different histotypes and natures in the same organ.