Thymidylate synthase (TYMS), which catalyzes the conversion of deoxyuridine monophosphate to deoxythymidine monophosphate, is a central enzyme in the folate metabolic pathway. Epidemiological studies have evaluated the association between TYMS gene polymorphisms and breast cancer susceptibility; however, the published data are still inconclusive. To derive a more precise assessment of this relationship, we performed a meta-analysis based on currently available data by searching PubMed, EMBASE databases, and the Cochrane Library. A total of 10 eligible studies were identified for the TYMS TSER polymorphism (six studies with 2,718 cases and 3,423 controls) and for the TYMS TS3'-UTR polymorphism (five studies with 1,969 cases and 2,290 controls). The overall odds ratio (OR) and the corresponding 95% confidence interval (CI) showed a statistical association between the TSER polymorphism and breast cancer risk under homozygote comparison (2R/2R vs. non-2R/non-2R; OR 1.25; 95% CI 1.04-1.50), allele contrast (2R vs. non-2R; OR 1.09; 95% CI 1.01-1.19) and the recessive model (OR 1.19; 95% CI 1.01-1.39). In the subgroup analysis by ethnicity, a statistically significant increase in cancer risk was found among Caucasians for homozygote comparison (OR 1.31; 95% CI 1.10-1.57), the allele contrast model (OR 1.12; 95% CI 1.02-1.23) and the dominant model (OR 1.40; 95% CI 1.00-1.95). For the TS3'-UTR polymorphism, significant effects were shown using the allele contrast model (OR 1.33; 95% CI 1.03-1.73). However, the TS3'-UTR polymorphism increased breast cancer risk among Asian women (del6 vs. ins6; OR 1.41; 95% CI 1.01-1.98) but not Caucasian women using the homozygote comparison. In conclusion, our meta-analysis suggests that the TSER polymorphism may increase susceptibility to breast cancer in the Caucasian population and the TS3'-UTR polymorphism may be a genetic determinant for developing breast cancer in the Asian population; therefore, ethnic background should be carefully considered in further studies.