Objective: The purpose of this study was to investigate the expression of MUC1, MUC2, MUC5AC and MUC5B in breast mucinous lesions. Methods: Immunohistochemical staining of MUC1, MUC2, MUC5AC, MUC5B and synaptophysin was performed in 78 cases of mucinous carcinoma (MC), 36 cases of mucocele-like lesions (MLL) and 13 cases of solid papillary carcinoma (SPC). MC was classified as type A or type B and MLL was classified as MLL, MLL with atypical ductal hyperplasia and MLL with ductal carcinoma in situ. Results: MUC1 was expressed in MC type A and MLL with luminal/apical pattern, while MC type B and SPC showed membrano-cytoplasmic expression of MUC1 (p < 0.001). A luminal/apical or luminal/apical + cytoplasmic pattern of MUC2 expression was observed in MC type A, while MC type B and SPC showed membrano-cytoplasmic MUC2 expression (p < 0.001). On MUC5B staining, MC type A and MLL were negative, while MC type B and SPC showed membrano-cytoplasmic expression (p = 0.011). The positive rate for synaptophysin was higher in MC type B and SPC than in MLL and MC type A (p = 0.001). Conclusions: Similar MUC phenotypes were observed between MLL and MC type A and between MC type B and SPC.