Objective:To evaluate the serum thymidine kinase 1(TK1)as a tumor marker for early tumor detection and monitoring chemotherapy effect on breast cancer patients operated. Methods:A sensitive chemiluminescence dot-blot assay was used to detect serum TK1 level in breast cancer patients(48 cases),including post-treated breast cancer patients(14 cases). Results:Forty eight cases had the pathological stage data. In order to exam the effect of chemotherapy,14 cases were chose to be followed-up for 1~3 months. Serous TK1 level in 10 of 14 cases was decreased to the level of healthy volunteers;four in 14 cases had a increased serous TK1 level,and one of them progressed bone metastasis one year later. Conclusion:Serous TK1 level has a correlation to the proliferation of breast cancer cell. Serum TK1 is a favorable and helpful marker for monitoring the response of chemotherapy.