UBC9 protein (E2-conjugating enzyme) plays a key role in post-translation modification named sumoylation. Proteins, which are sumoylated take part in many cellular processes including cell growth, maintaining the genome integrity and stability and cancer development. The aim of this study was to investigate an association between three polymorphisms of the UBC9 gene: c.73G>A (rs11553473), c.430T>G (rs75020906) and g.1289209T>C (rs7187167) and a risk of ductal breast cancer occurrence. We performed a case-control study in 181 breast cancer cases and 277 controls using PCR-RLFP and ASO-PCR. In the case of the 430T>G polymorphism of the UBC9 gene lack of variability suggests that there is not a polymorphic site in polish population. We observed that a risk of breast cancer occurrence is elevated in patients with the G/A genotype (OR 5.03; 95% Cl 3.05-8.28), the A/A genotype (OR 11.3; 95% Cl 4.24-30.3) and the A allele (OR 6.86; 95% Cl 4.43-10.6) of the c.73G>A polymorphism. In the case of the g.1289209T>C polymorphism we found a correlation between estrogen receptor (ER) expression and the T/T genotype (OR 0.22; 95% Cl 0.07-0.64) and the T allele (OR 0.53; 95% Cl 0.32-0.88). We also found a correlation between the T/T genotype (OR 4.13; 95% Cl 1.21-14.1) and the T allele (OR 2.09; 95% Cl 1.07-4.08) of the g.1289209T>C polymorphism with triple negative breast cancer. Our results suggest that the variability of the UBC9 gene can play a role in breast cancer occurrence.