Abstract: Objective To explore the clinical significance of strongly positive expression (+++) of mucin1 (MUC1) for prognosis and individual treatment in different immunophenotypes of breast cancer. Methods Three hurdred and thirty-five cases of breast cancer were categorized as follows: ER+/PR+,HER2-; ER+/PR+,HER2+; ER-,PR-,HER2+ and ER-,PR-,HER2- subtype. The expression levels of ER,PR,HER2 and MUC1 were detected by mean of immunohistochemistry and the relationship between the strongly positive expression of MUC1 and prognosis of breast cancer was analyzed. Results The strongly positive rate of MUC1 in 335 cases was 46.3 %, 5-year overall survival rates(OS) of patients with strongly positive expression of MUC1 was lower (P<0.05).In 335 cases, ER+/PR+,HER2- subtype was 130, ER+/PR+,HER2+ subtype was 64, ER-,PR-,HER2+ subtype was 67 and ER-,PR-,HER2- subtype was 74. The strongly positive rate of MUC1 of four subtypes was 59.2%、56.3%、32.8% and 27.0%, respectively. The strongly positive rate of MUC1 has related to the immunophenotypes of breast cancer（P<0.01）.5-year overall survival rates(OS) of patients with strongly positive expression of MUC1 was lower in ER+/PR+,HER2- and ER-,PR-,HER2+ subtype (P<0.05) by group analysis of prognosis. Conclusion The strongly positive expression of MUC1 was related to the immunophenotypes of breast cancer and played different role in prognosis of different immunophenotypes of breast cancer. The prognosis of patients with MUC1 strongly positive expression was poorer in ER+/PR+,HER2- and ER-,PR-,HER2+ subtype.