Pancreatic cancer has a poor prognosis, and it often causes duodenal obstruction and obstructive jaundice associated with tumor invasion. Self-expandable metal stent (SEMS) placement is useful for duodenal obstruction. Pancreatic cancer can occur in the uncinate process, which may lead to malignant obstruction in the third portion of the duodenum. However, the upper gastrointestinal endoscope often cannot reach the third portion of the duodenum, and SEMS placement is sometimes difficult. We report a case of successful SEMS placement with a colonoscope for the obstruction of the third portion of the duodenum due to uncinate process cancer. A 67-year-old Japanese male was referred to our hospital for palliative treatment of unresectable pancreatic cancer. He complained of anorexia and vomiting and was admitted to our hospital. Computed tomography (CT) scans showed the tumor with delayed enhancement in the pancreatic uncinate process. Esophagogastroduodenoscopy (EGD) and gastrografin enema revealed the stenosis caused by tumor invasion in the third portion of the duodenum. The stenosis was thought to cause his symptom. PCFQ260AZ endoscope (Olympus, Tokyo, Japan) was able to reach the stenosis, and a 22 mm × 80 mm uncovered SEMS (Niti-S, Taewoong Medical, Seoul, South Korea) was placed beyond the stenosis. After SEMS placement, his symptoms disappeared. Uncinate process cancer is located close to the third portion of the duodenum and caused the obstruction there. We should be cautious about this, and a colonoscope is useful for SEMS placement for malignant obstruction in the third portion of the duodenum.