Abstract: Objective To investigate the relationship between polymorphisms of thymidylate synthase（TYMS）and the efficacy of pemetrexed-based chemotherapy in advanced non-small cell lung cancer（NSCLC）. Methods A total of 67 patients with stage ⅢB-Ⅳ NSCLC received pemetrexed monotherapy or pemetrexed plus platinum combination were enrolled in this study. Pemetrexed was intravenously administrated 500mg／m2 d1，and cisplatin 75mg／m2 or carboplatin AUC 5 d1. Every 3 weeks was a cycle. The genomic DNA extracted from peripheral blood mononuclear cell was used to examine the polymorphisms of TYMS in the 5’and 3'untranslated region（UTR） using PCR and PCRRFLP. Due to PCR results，we analyzed the relationship between TYMS polymorphisms and the efficacy of pemetrexedbased chemotherapy. Results The efficacy of the 67 advanced NSCLC patients could be evaluated. The response rate（RR）and disease control rate（DCR）were 28.4％ and 76.1％. The median progressionfree survival was 3.5 months. There was no significant difference of RR and DCR among the three 5’UTR genotypes of TYMS polymorphism，as well as the three 3’UTR genotypes of TYMS polymorphism. Conclusion The polymorphism of TYMS and efficacy of pemetrexedbased chemotherapy in patients with advanced NSCLC had no obvious relations. The relationship between TYMS polymorphisms and the efficacy of pemetrexed-based chemotherapy will be confirmed by further study.