Sarcomatoid carcinomas (carcinosarcomas) are rare lesions in the hepatobiliary pancreatic system. We present an extremely rare case of sarcomatoid carcinoma of the common bile duct. The tumor showed a biphasic pattern of intermixed carcinomatous (adenocarcinoma) and sarcomatoid elements (spindle and giant cells). By immunohistochemical staining, cytokeratin and vimentin were demonstrated in the sarcomatoid component. The proliferative activity and the oncoproteins expressed by the tumor were investigated by the PCNA, Ki-67, p53 and Bcl-2 in different tumor fields. Overall, the intensities of PCNA and p53 were moderate in the sarcomatoid component, but mild in the carcinomatous component. However, Ki-67 and Bcl-2 were both negative in the carcinomatous and sarcomatoid components. The possible histogenensis of sarcomatoid carcinoma of the common bile duct is discussed. We report upon an additional extremely rare case of sarcomatoid carcinoma arising in the common bile duct together with its immunohistochemical characteristics, and give details of its proliferative activity and oncoprotein expression.