Transcription factor 21 (TCF21) functions as a tumor suppressor and is inactivated in several types of cancer. The purpose of this study is to investigate whether TCF21 genetic polymorphisms(rs2327429 T>C, rs2327430 T>C, rs2327433 A>G, rs12190287 C>G, rs7766238 G>A, rs4896011 T>A) are associated with the risk of breast cancer in Chinese women. Logistic regression analyses showed that TCF21 rs12190287 polymorphism was significantly associated with the reduced risk of breast cancer. Stratified analyses based on pathological type indicated that TCF21 rs12190287 polymorphism was only associated with the reduced risk of infiltrative ductal carcinoma. Real-time quantitative PCR analyses revealed that compared with those carrying rs12190287 CC genotype, subjects with GG genotype had higher expression levels of TCF21 mRNA in normal breast tissues. Furthermore, luciferase activity assay showed that the rs12190287 G allele weakened the binding affinity of hsa-miR-224 to TCF21 3' UTR. These findings suggest that TCF21 rs12190287 polymorphism can regulate TCF21 expression and may serve as a potential marker for genetic susceptibility to breast cancer.