Abstract: Objective : To investigate the reason of the 5-FU drug resistance, and to prove deeply the influence of TS in colon carcinoma with the level of cell culture. and to evaluate the expression of TS could be as a chemotherapeutic efficacy index in patients with colon carcinoma. Methods : To proceed the 5-FU drug susceptibility test with MTT method to 30 cases in vitro culture colon carcinoma cell; to be examined by SP immunohistochemical staining and observed the expression of TS;and then compare with them. The expression of TS in 60 cases with colon carcinoma and their control cases were examined by SP immunohistochemical staining. Results : In vitro culture colon carcinoma cells corresponding high-expression of TS the sensibity to 5-FU delay obviously than the low-expression. The level of TS in normal colon tissues was higher than that in colon carcinoma. The level of TS in well-differentiated colon carcinoma was higher than that in poor-differentiated cases. There was an inverse association between the level of colon carcinoma TS expression and clinical prognosis,the level of TS showed no correlation with sex and lymph node metastases. Conclusions : The positive expression of TS has a instruction significance in colon carcinoma patients at the election of chemistry drug, it can be as a 5-FU based chemotherapeutic efficacy and clinical prognosis index in patients with colon carcinoma.