Rationale: Gallbladder duplication is a rare congenital disorder, which could cause an increasing risk of complications during surgery. The coexistence of cholangiocarcinoma with double gallbladder is extremely rare, which might lead to an even higher possibility of misdiagnosis and postsurgery complications. Patient concerns: A 58-year-old female was presented with abdominal pain and jaundice. Abdominal ultrasonography showed duplication of gallbladder. one of which with a thickened wall and a rough surface. This was also confirmed by an abdominal computed tomography (CT), magnetic resonance imaging (MRI) and magnetic resonance cholangiopancreatography (MRCP) scan. During the surgery, we found a tumor inside one bile duct. The postsurgery pathology showed adenosquamous carcinoma. Diagnoses: Gallbladder duplication, cholangiocarcinoma. Interventions: The tumor was removed by surgery. Outcomes: The patient died of tumor relapse six months after surgery. Lessons: This is the first reported case with coexistence of gallbladder duplication and cholangiocarcinoma, which was diagnosed by abdominal ultrasound, CT and MRCP, as well as further confirmed in surgery and pathology. This case emphasized the importance of a thorough examination of gallbladder before surgery, especially in those cases with suspected double gallbladder, since each gallbladder could have the possibility of an independent cholangiocarcinoma.