Cancer pain often makes patient's performance status worsen and is one of the difficulties in anti-cancer therapy. We report a case of unresectable advanced pancreatic cancer with cancer pain, which was treated by matrix-type transdermal fentanyl following slow-releasing oxycodone, which caused severe constipation. Rotation to matrix-type transdermal fentanyl (Durotep MT 2.1 mg) releaved severe constipation as well as cancer pain. The patient could take gemcitabine-based chemotherapy. Low-dose matrix-type transdermal fentanyl (Durotep MT 2.1 mg) is useful for opioid rotation from low-dose morphine or oxycodone with uncontrolled side effects, and it contributes to continuation of anti-cancer therapy.