Manganese superoxide dismutase plays a role in breast tumor cell growth, which depends on its constitutive expression. However, the mechanisms responsible for the regulation of constitutive SOD2 gene expression at different malignant phenotype in breast cancers remain to be determined. The present study reports the identification and characterization of a DNA sequence located in the proximal promoter of the SOD2 gene, which forms a complex with a nuclear protein from breast tumor MCF-7 cells. Purification of this complex showed that it contained DDB2 (damaged DNA binding 2), a well known protein involved in nucleotide excision DNA repair and cell cycle regulation. Functional analysis of the proximal promoter of the SOD2 gene or modulation of DDB2 expression allowed us to demonstrate that DDB2 regulates negatively the constitutive expression of the SOD2 gene in breast cancer cells. We demonstrate that the binding of DDB2 was associated with the loss of acetylated H3 histones and the decrease in the binding of Sp1 but not AP-2alpha transcription factors to the SOD2 proximal promoter. In addition, we show that DDB2 exerts, at least in part, a control of breast cancer cell growth through its negative regulation of constitutive expression of the SOD2 gene. For the first time, these data give supporting evidence that DDB2 is a new transcriptional regulator, and they provide insight into the molecular function of breast cancer cell growth, which will have an important clinical interest.