We describe a unique case of intra-abdominal textiloma (granuloma due to a retained foreign body), which mimicked a gastric tumor on preoperative imaging studies. A 78-year-old asymptomatic patient with a past history of a gastrectomy was referred for evaluation of an intra-abdominal mass lesion, which was incidentally observed on a computed tomography (CT) scan. Repeated CT with a higher resolution demonstrated a 5-cm heterogeneously enhanced mass with a distinct feeding artery. These findings were all compatible with a tumorous lesion originating in the gastric remnant, most likely gastric gastrointestinal stromal tumor. A diagnosis of textiloma was immediately made during surgery, and it was confirmed pathologically postoperatively. The feeding artery that appeared on CT images, which was a major reason for the false diagnosis, was considered to have resulted from a slow but continuous inflammation reaction around the retained surgical sponge. Surgeons should therefore always take the possibility of textilomas into consideration even with typical tumorous characteristics on preoperative imaging studies, especially in patients with a history of prior abdominal surgery.