Mixed adenoneuroendocrine carcinoma (MANEC) is defined as having morphologically recognizable adenocarcinoma and neuroendocrine carcinoma (NEC) components, and is rare in the bile duct. We report herein on a case of MANEC of the common bile duct diagnosed with brush cytological examination using endoscopic retrograde cholangiopancreatography. It has been reported that the NEC component of MANEC of the bile duct defines the prognosis. Therefore, it is important to detect the NEC component. Careful observation of brush cytological specimens from the bile duct can lead to a cytodiagnosis of MANEC.