The forkhead box transcription factor Foxo3a has been implicated to play a critical role in various cancers by suppressing tumor growth. Recent studies have identified Foxo3a as a key regulator of Estrogen Receptor-α (ERα). In the present study, we examined the expression of Foxo3a, and investigated its clinical significance and correlation with ER and prognostic role in patients with breast cancer. Immunohistochemical analysis was performed on tumors from 70 breast cancer patients. Interpretable Foxo3a expression was analyzed along with major clinicopathologic variables, and a comparison was made with corresponding 5-year clinical follow-up data. Foxo3a protein expression correlated with ER positivity (P<0.001), histologic grade (1, 2) (P = 0.002), axillary lymph node negativity (P<0.001) and TNM stage (1, 2) (P<0.001). Moreover, the Kaplan-Meier survival curves of the study population showed that a high expression level of Foxo3a was significantly correlated with long-term survival (P<0.0001). In a multivariate analysis, Foxo3a expression was identified as a favorable independent prognostic factor in overall survival (P = 0.038). In conclusion, our results indicated that Foxo3a expression is a favorable prognostic marker in breast cancer. In addition, Foxo3a staining could potentially be used in patient stratification in conjunction with other prognostic markers.