Abstract: Objective: To study the expression of estrogen receptor subtype ERα/β gene mRNA and ERα protein in female breast cancer,and to investigate the expression significance of ER subtype by analyzing the relationship between the expression of ER subtype and the clinic pathologic behavior of breast cancer.Methods: Reverse transcription polymerase chain reaction and immunohistochemistry S-P methods were used to detect the expression of ERα/β gene mRNA and ERα protein in 52 fresh breast cancer samples and 19 fresh breast fibroadenoma samples.Results: The total positive rate of ERβ mRNA was 51.9% in breast cancer,which was significantly higher than that in breast fibroadenoma(P<0.05).The positive rate of ERα mRNA alone in breast fibroadenoma was 63.2%,which was significantly higher than that in breast cancer(P<0.05).The coexpression rate of ERα and ERβ mRNA in breast cancer was 51.9%,higher than that(15.8%) in breast fibroadenoma(P<0.05).The phenotype of coexpression ERα and ERβ in breast cancer was associated with positive lymph node(P<0.05),and there was a trend toward higher grade.There was no significant difference between the positive rate of ERα protein in breast cancer and breast fibroadenoma.Conclusions: The coexpression of ERαand ERβ in breast cancer may be a poor prognostic factor for patients with breast cancer.