Objective: To investigate the expression of tumor specific protein 70 (SP70) in breast cancer tissues and blood to eva- luate whether SP70 could differentiate the benign breast tumor and malignant breast tumor. Methods: The SP70 expressions of paraffin sections in the tissues of 65 malignant breast tumors and 60 benign breast tumors were studied by immunohistochemistry(IHC) technique. The levels of SP70 in the serum of 58 malignant breast tumors, 62 benign breast tumors and 60 healthy subjects were studied by enzyme-linked immuno sorbent assay(ELISA). Results: The expression positive rate of SP70 was 55.38% in the tissues of malignant breast tumors, whereas, only 15.00% in benign breast tumors. The difference was statistically significant (χ2=23.846, P<0.001). The serum SP70 level of patients with malignant breast tumors was significantly higher than that in patients with benign breast tumors and healthy controls(F=11.884，P<0.001). The sensitivity of serum SP70 for diagnosis of malignant breast tumors was significantly higher than that of serum CA153 (53.45% vs. 44.82%), a significant association between serum SP70 and serum CA153 had not been found (r=0.132，P=0.324). The combine of serum SP70 and serum CA153 could significantly improve the sensitivity(84.38%). Conclusion: SP70 may be used to differentiate diagnosis of malignant breast tumors and benign breast diseases.