Here we report a case of perforation of the small intestine by metastasis of cancer of the upper gingiva. The patient was an 86-years-old man who had squamous cell carcinoma of the upper gingiva. The patient enforced partial maxillary resection. And abdominal pain during Radiation therapy. A CT scan taken for the purpose of close examination revealed confirming perforation of the gastrointestinal tract. Surgery was performed immediately. Peritoneal perforation and peritoneal dissemination due to a small intestine tumor were observed. Microscopic findings at this site confirmed a diagnosis of metastatic squamous cell carcinoma in the small intestine from the upper gingiva. If gastrointestinal symptoms appear in a patient with advanced oral cancer, a differential diagnosis of metastasis to the gastrointestinal tract should be kept in mind.