Abstract: Objective To investigate the expression of RASSF1A gene in human breast cancer and evaluate their clinical significance.Methods RT-PCR was used to detect the expression of RASSF1A mRNA in 51 cases of breast carcinoma,30 cases of normal tissue adjacent to breast cancers and 12 cases of breast benign diseases.Results (1)There is no difference between the expression of RASSF1A mRNA in normal tissue adjacent to breast cancers and breast benign diseases(P＞0.05).The deficient expression rate of RASSF1A mRNA in breast cancer is 51.0%(26/51)and lower than normal tissue adjacant to breast cancers and breast benign diseases(P＜0.01);(2)In breast cancer,loss of RASSF1A mRNA expression had significantly association with lymph node metastasis(P＜0.05);(3)Low or loss of RASSF1A mRNA expression in breast cancer had no association with age of patients,tumor size,tumor pathological type,the clinical TNM stage,ER,PR and HER-2 expressions(P＞0.05).Conclusion Loss of RASSF1A gene expression may play an important role in tumor progression,and may be considered as avaluable marker for predicting the prognosis in breast cancer.