A 67-year-old man with small cell lung cancer was referred to our department. The patient had received chemotherapy for lung cancer and complained of no specific symptoms. Follow-up positron emission tomography (PET) showed a new duodenal lesion. Immunohistochemistry (IHC) with the specimens obtained by endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) showed that the lesion was metastasis from lung cancer. These results contributed to the subsequent treatment strategy. Gastrointestinal metastasis from lung cancer diagnosed during the patient’s lifetime is rare. This is the first case of asymptomatic duodenal metastasis from small cell lung cancer diagnosed by EUS-FNA