Objective:To investigate the correlation between histone deacetylase 1(HDAC-1) expression and clinical pathological significance. Methods:HDAC-1 protein expression in 120 cases of breast cancers and a control group of 20 cases of breast hyperplasia in breast tissue were examined by immunohistochemical, and the relationships between HDAC-1 protein and clinical features and conventional detection index of ER, PR, HER-2 were analyzed. Results:Among 120 patients with breast cancer, HDAC-1 was high expressed in 43 cases(35.83%), but HDAC-1 was low expressed or not in control group, the difference was significant. HDAC-1 in breast cancers with high expression was significantly correlated with age, clinical stage, HER-2, expression(all P < 0.05): patients who were older than 50 years(49.50%), in clinical period of stage Ⅲ ~ Ⅳ(64.28%), or HER-2(55.26%) was positive correlation with HDAC-1 high expression, but HDAC-1 expression was negatively correlated with tumor size, histological grade, with or without lymph node metastasis, and cancer tissues and adjacent tissues without infiltration of lymphocytes, and ER(33.89%) or PR(39.28%) expression(P > 0.05). Conclusion: HDAC1 protein plays an important role in the development of breast cancer, and HDAC-1 inhibitor is expected to become a new targeting drug for breast cancer treatment.