The role of Wilms' tumor 1 (WT1) in breast cancer and the relationship between WT1 expression and clinicopathological factors, molecular subtypes and prognosis of breast cancer patients have not been clarified to date. We used publicly available microarray datasets of 266 early breast cancer patients to perform bioinformatics analysis on the relationship between WT1 mRNA expression and breast cancer. Results showed that WT1 mRNA expression was correlated with higher histological grades, ER-negative and basal-like and ERBB2 molecular subtypes in breast cancer. With regard to disease-free survival analysis, the WT1 high expression group showed worse prognosis than the low expression group in univariate analysis, and WT1 was demonstrated to be an independent prognostic indicator in multivariate analysis. This study confirms an oncogenic role of WT1 and demonstrates a possible relation between WT1 and progression of breast cancer.