The patient was a 43-year-old man. An upper gastrointestinal endoscopic examination revealed a gastric submucosal tumor(SMT)-like, elevated 8-mm lesion in the greater curvature of the upper body of the stomach. It was diagnosed as spindle cell tumor on the basis of biopsy findings, and a gastrointestinal stromal tumor(GIST)was suspected. Various immunohistochemical staining techniques were used; however, a definitive diagnosis could not be achieved. There was no evidence of distant metastasis even on thoracoabdominal computed tomography imaging; thus, the patient was referred to our department for definitive diagnosis and surgical treatment. Laparoscopic local gastrectomy with concomitant intraoperative gastroscopy was performed. Pathological examination of the resected specimen showed a type Ⅱc-like lesion with a maximum diameter of 6 mm in the mucosal layer along with spindle cell proliferation. Immunostaining was negative for c- kit, DOG1, CD34, S-100, SMA, WT-1, desmin(N), EMA, and keratin(pan)and positive for β-catenin, Bcl-2, and vimentin; furthermore, low Ki-67(MIB-1)expression was detected. Therefore, GIST, solitary fibrous tumor, leiomyoma, leiomyosarcoma, desmoid tumor, spindle cell carcinoma, and synovial sarcoma were excluded, and an unclassifiable spindle cell tumor arising from the gastric mucosa was diagnosed. The patient has remained recurrence-free for 1 year and 8 months post-operatively and is currently under careful outpatient follow-up.