Objective To evaluate the value of immunoblotting in the detection of serum thymidine kinase 1 (TK1) in breast tumor patients. Methods TK1 in sera from breast tumor patients, non tumor patients and healthy volunteers were determined with immunoblotting assay.Results The levels of TK1 in breast cancer patients before operation, patients with benign breast tumor, non tumor patients, and healthy volunteers were (39.3? 33.9), (3.7?3.9), (1.7?0.5) and (1.4?0.5) pmol/L respectively. The value of TK1 was higher in malignant and benign breast neoplasms patients than in healthy volunteers. However, no significant difference in the TK1 level was found between breast cancer patients without metastasis after operation, non tumor patients, and healthy volunteers.Conclusions The immunoblotting of TK1 by anti TK1 antibody is a sensitive and specific assay. It can be used to monitor and predict the efficiency of the therapy as well as the breast neoplasms progression during clinical course.