Inflammatory myofibroblastic tumor of the stomach is a rare tumor-like, benign disease with an uncertain pathogenesis. A 15-year-old male presented with epigastric pain. Endoscopic ultrasonography revealed a 2.3 cm sized ovoid intramuscular mass in the lower body of the stomach at the lesser curvature. Histologically, the tumor was composed of smooth muscle actin positive- and vimentin positive spindle cells and there were a large number of lymphocytes, plasma cells and histiocytes in the fibrotic background. The spindle cells were also positive for ALK1, but negative for EBV in situ hybridization.