Objective：To detect the expression and significance of estrogen receptor-related receptor（ERR） α mRNA and protein in breast cancer and breast para-carcinoma tissues and to further discuss the correlation between ERR α and breast cancer clinical pathological index（（estrogen receptor（ER），progestin receptor（PR），human epidermal growth factor receptor-2（Her-2），P53） as well as the grade and classification of breast cancer. Methods：Expression of ERRα in 87 breast cancer tissues and the corresponding breast para-carcinoma tissues were detected by immunohistochemistry and reverse transcription PCR（RT-PCR），Western blot respec－tively and their relationship with the clinical pathological characteristics was analyzed. Results：Expression of ERR α mRNA and pro－tein in breast cancer tissues was higher than that in breast para-carcinoma tissues（P<0.05）. Expression of ERR α was correlated with ER，Her-2，degrees of differentiation，tumor size and metastasis of the lymph nodes but was not correlated with patient’s age，PR and P53. Conclusions：High expression of ERR α may serve as a biomarker of poor prognosis in breast cancer and it may provide new thought for the diagnosis and treatment of breast cancer.