The aim of this study was to assess the expression of metabolism-related proteins including glucose transporter 1 (Glut-1), carbonic anhydrase IX (CAIX) and monocarboxylate transporter 4 (MCT4) in breast mucinous carcinoma and to evaluate the implications of the results.Immunohistochemical staining for Glut-1, CAIX, and MCT4 was performed on tissue sections from 59 cases of mucinous carcinoma to evaluate the association between the expression of metabolism-related proteins and clinicopathologic factors. Mucinous carcinoma was subclassified into type A and type B according to histopathological characteristics.Of the 59 patients, 35 patients (59.3%) were type A mucinous carcinoma and 24 patients (40.7%) were type B mucinous carcinoma. Stromal expression of MCT4 was significantly associated with a high histologic grade (p=0.022) and type B mucinous carcinoma (p=0.016). There were significant positive correlations between the expression of Glut-1, CAIX and tumoral expression of MCT4 (p<0.05).We assessed the expression of metabolism-related proteins including Glut-1, CAIX, and MCT4 in breast mucinous carcinoma and found that the stromal expression of MCT4 was higher in type B mucinous carcinoma than in type A, which reflected a difference in the tumor microenvironment.