Mixed adenoneuroendocrine carcinoma (MANEC) of the biliary tract is rare. Here, the authors report a case of MANEC of the gallbladder, in which neuroendocrine carcinoma (NEC) exhibited collision and sharp separation from a moderately differentiated adenocarcinoma; these two tumor components made up of more than 30% of the entire tumor, respectively. The tumor metastasized to liver and one lymph node, and the hepatic metastatic component was from an neuroendocrine tumor (NET), while the lymphovascular invasion and lymph node metastasis was attributed to adenocarcinoma. Ki-67 im-munostaining (>50%) and numerous mitotic counts showed the NET exhibited high proliferative activity. Because the neuroendocrine component in biliary MANEC defines prognosis, its identification is of considerable importance.