Fluorouracil is well known as a standard chemotherapeutic drug in breast cancer and other cancers that is converted to flurodeoxyuridine monophosphate (FdUMP) and leads to the inhibition of thymidylate synthase (TS) in tumor tissues. The role of this enzyme is the catalysis of the methylation from deoxyuridine monophosphate (dUMP) to deozythymidine monophosphate (dUMP), which is a very important process for DNA synthesis in tumor tissues, Increased level of TS protein correlates inversely with sensitivity and response to 5 FU in human cancer cell lines, Authurs evaluated the TS expression level using the immunohistochemical staining and analyzed their relationship with other prognostic factors and clinical outcome of breast cancer patients. The results were as follows; 1) TS level was not related histopathologic stage, involvement of axillary lymph nodes, estrogen receptor, progesterone receptor, recurrent type, primary tumor and recurrent tumors, disease free survival rate. 2) TS level was associated with c-erbB2 overexpression. 3) c-erbB2 overexpression was related with recurrence rate. 4) TS level appeared to be related with recurrence rate. So we conclude the TS level can be used as an independent prognostic predictor in breast cancer patients.