Abstract: Objective To investigate the significance of TYMS and ERCC1 gene polymorphism in peripheral venous blood in evaluating chemotherapeutic effect on outcomes of patients with gastroenteric tumor. Methods Experimental groups: (1)Specimens of patients with non-chemotherapy groups: peripheral blood group and tumor tissue group. (2)Specimens of patients with chemotherapy groups: effective chemotherapy group and ineffective group. The genotypes of TYMS and ERCC1 in peripheral blood and tumor tissue were detected by PCR and PCR-RFLP. Results In peripheral blood and tumor tissues of patients with nonchemotherapy, the detection rates of 3R/3R, (2R/2R, 2R/3R) genotypes of TYMS were 72.09% and 27.91% (P<0.01), those of C/C, (T/T, C/T) genotypes of ERCC1 were 81.39% and 18.61% (P<0.01). The detection rates of 3R/3R, (2R/2R, 2R/3R) genotypes of TYMS in patients with chemotherapy were 65.79% and 34.21%; those of C/C, (T/T, C/T) genotypes of ERCC1 were 63.16% and 36.84%. Chemotherapy response rates of TYMS genotype carriers were 18% and 57.69%; those of ERCC1 were 47.91% and 3.57%. Genotypes of TYMS and ERCC1 had correlation with chemotherapy response rate (P<0.01). Chemotherapy response rates between the genotypes were different(P<0.01). Conclusion Tumor tissues could be replaced by peripheral blood sample in detecting TYMS and ERCC1 polymorphism which could be used to evaluate the efficacy of 5-Fu and platinum drugs.