Recent preclinical data suggest that androgen receptor (AR) signaling plays a significant role in subsets of breast cancer. Clinical trials testing AR-targeting therapies in breast cancer have been conducted. Assessment of AR-signal in breast cancer tissue maybe useful for treatment selections. Prostate specific antigen (PSA) is the product of an androgen-responsive gene. Serum PSA (sPSA) can be detected in women by a highly sensitive assay although the concentration is much lower than that observed in males. We investigated if sPSA reflects tumor biology, including AR signaling in breast cancer patients. In this study, 132 healthy controls and 144 breast cancer patients were enrolled. sPSA was evaluated by the chemiluminescent enzyme immunoassay (CLEIA) method. Correlations between sPSA and the various clinicopathological factors were analyzed. In post-menopausal state, sPSA detection rate was significantly higher in breast cancer patients compared with controls (27.4% vs 11.3%: p = 0.0090), but not in the whole cohort (29.2% vs 25.8%: p = 0.5265) or pre-menopausal subgroup (37.0% vs 42.6%: p = 0.6231). In post-menopausal breast cancer cases, higher sPSA value was associated with clinic-pathological factors including the expression of AR protein in primary legion. In a correlation analysis of quantitative data limited to post-menopausal metastatic breast cancer (MBC), sPSA was positively, albeit weakly correlated with clinic-pathological features including serum testosterone levels and AR positivity. Our data suggest that sPSA may reflect tumor biological properties including AR activity in post-menopausal breast cancer.