Primary gastric rhabdomyosarcoma is extremely rare. An 87-year-old man visited our clinic with a chief complaint of abdominal pain. Computed tomography (CT) and 18 F-fluorodeoxyglucose positron emission tomography-CT (FDG-PET/CT) revealed a massive tumor originating from the muscularis propria of the stomach along with splenic vein tumor thrombosis. We diagnosed the patient with primary gastric rhabdomyosarcoma by an endoscopic ultrasound-guided fine-needle aspiration/biopsy (EUS-FNA/B).