Complete surgical resection of the tumor is the sole approach to improve the cure rate of patients with intrahepatic cholangiocarcinoma-mass forming type (ICC-MF). Although patients are treated by curative resection, many of them show poor outcome. Mucin (MUC)4 expression has been implicated as a marker for diagnosis and progression of pancreatic adenocarcinomas, but there is no study of the relationship between MUC4 expression and patient's prognosis in ICC-MF. In the present study, we examined the expression profile of MUC4 in ICC-MF tissue from 27 patients using immunohistochemistry. MUC4 was expressed in the carcinoma tissues of 10 (37%) of the 27 ICC-MF tumors, whereas it was not expressed in normal liver tissue. Because MUC4 is an intramembrane ligand for receptor tyrosine kinase ErbB2 and is related with regulation of p27, we also compared the MUC4 expression with ErbB2 and p27 expressions in ICC-MFs. The patients with MUC4 and ErbB2 double positive expression showed a short survival period compared to non-expressing patients. MUC4 and p27 showed no relationship. The univariate analysis showed that tumor size, intrahepatic metastasis, lymph node metastasis, MUC4 expression, and MUC1 expression were statistically significant risk factors affecting the outcome of the patients with ICC-MF. The multivariate analysis demonstrated that MUC4 expression, as well as surgical margin, were statistically significant independent risk factors. In conclusion, the results suggest that expression of MUC4 in ICC-MF is a new independent factor for poor prognosis and is a useful marker to predict the outcome of the patients with ICC-MF.