Abstract: Objective: To investigate the correlation of MDM2 SNP309 polymorphism with breast cancer risk in Chinese women. Methods:The polymorphism of MDM2 SNP309 was detected by PCR-restriction frag-ment length polymorphisms assay (PCR-RFLP) in 698 women with primary breast cancer and 525 healthy controls. Results: Compared with the T/T genotype, the G allele (T/G or G/G) was not associated with an in-creased risk of breast cancer in the entire population studied (T/G, adjusted OR=1.2, 95% CI: 0.8~1.6, P=0.30; G/G, adjusted OR=1.0, 95% CI:0.7～1.5, P=0.88). Among postmenopausal women, the G allele (T/G or G/G) was significantly associated with an increased risk of breast cancer (T/G, adjusted OR=1.8, 95% CI: 1.2～3.0, P=0.011 ; G/G, adjusted OR=1.9, 95% CI: 1.2～3.3, P=0.014 ). But this association was not ob -served among premenopausal women. Conclusion:MDM2 SNP309 heterozygous T/G genotype and homozy-gous mutant G/G genotype increase breast cancer risk in postmenopausal Chinese women.