Little is known about the lung adenocarcinoma metastasize to the duodenum and small intestine. We encountered a case of duodenum and small intestine metastasises by showing abnormal uptake of FDG positron emission tomography (FDG-PET) and pathological examination. A 65-year-old man presented with chest abnormal shadow, that we made the diagnosis lung adenocarcinoma by bronchoscopic biopsy. FDG-PET showed abnormal uptake in duodenum and small intestine, so we performed upper gastrointestinal endoscopic examination and colonofiberscopy, while multiple duodenal tumors were observed in upper gastrointestinal endoscopic examinations. Three days after colonofiberscopy, he complained of abdominal pain. As a result of computed tomography of the abdomen, He was diagnosed with ileal perforation. An operation was undertaken and the surgical and pathological findings showed perforation by several small intestine metastasises from lung adenocarcinoma. Metastatic lung adenocarcinoma may have duodenum and small intestine metastasises. As Colonofiberscopy for a lung cancer patient with gastrointestinal metastasises might contribute to gastrointestinal perforation, we need to pay attention to it.