A 60-year-old male with increasing abdominal distension was admitted to The Fifth Affiliated Hospital of Guangzhou Medical University (Guangzhou, China). The abdominal sonogram exhibited a huge abdominal cystic-based mass with solid components in the left upper quadrant. A contrast-enhanced computed tomography scan of the abdomen revealed a large heterogeneous cystic solid tumor, but the source of the tumor could not be determined. The laparotomy demonstrated a huge cystic-based tumor with an integrated cystic wall, arising from the posterior wall of the gastric body. Multiple septa and ~3,500 ml of yellowish fluid were found in the cystic cavity. Pathological analysis showed that the tumor contained a mixture of polygonal and spindle cells. Immunohistochemical study indicated that the tumor cells were positive for CD117 and CD34. The final diagnosis was gastric gastrointestinal stromal tumor. The patient recovered well and no recurrence or metastasis was identified following a 12-month follow-up.