Objective:To analyze the relationship between ataxia telangiectasia mutated (ATM) single nucleotide polymorphism (SNP) at rs1801516 and rs1800054 and sporadic breast cancer (SBC) in Inner Mongolia.Methods:A total of 102 patients with SBC (72 Han and 30 Mongolian) who were admitted to the Affiliated Hospital of Inner Mongolia Medical University from January 2018 to September 2019 were prospectively collected as case group and 102 healthy women (72 Han and 30 Mongolian) during the same period as control group. 2 ml of venous blood was collected to extract DNA. According to the Single Nucleotide Polymorphism Database (dbSNP), the highly polymorphic sites rs1801516 and rs1800054 of ATM gene were selected. The polymerase chain reaction (PCR) and direct sequencing were used to detect the polymorphism of the two sites, and the correlation between the single nucleotide polymorphism of the two sites and the susceptibility of SBC in Inner Mongolia was analyzed. The potential association between clinicopathological factors and ATM gene polymorphism in patients with SBC in Inner Mongolia were explored.Results:GG, GA and AA genotypes were detected in rs1801516 locus of ATM gene. Only CC genotype was detected in the rs1800054 locus of ATM gene. There was no significant difference in the distribution of genotype frequency and allele frequency between Mongolian breast cancer group and Han breast cancer group, Mongolian control group and Han control group, Mongolian breast cancer group and Mongolian control group, Han breast cancer group and Han control group (all P>0.05). Logistic regression analysis showed that allele G was the susceptibility gene of SBC in Inner Mongolia ( OR: 1.775, 95% CI: 1.04-3.03, P=0.04). ATM rs1801516 polymorphism may be associated with increased risk of breast cancer in patients with mass diameter ≤2 cm and/or without lymph node metastasis (all P<0.05). Conclusions:The polymorphism of ATM gene rs1801516 and rs1800054 may not be significantly correlated with the risk of SBC in Inner Mongolia. The rs1801516 locus may be associated with increased risk of breast cancer in patients with mass diameter ≤2 cm and/or without lymph node metastasis. Gene G may be one of the susceptible genes of SBC in Inner Mongolia.