Homologous recombination has a major role in DNA double‐strand break repair. BMI‐1 has been associated with cell immortalization through the supression of INK4a/ARF locus, thereby allowing that DNA double‐strand breaks occur. However, the influence of BMI‐1 in homologous recombination markers is still poorly understood. Our objective was to evaluate the influence of BMI‐1 silencing on expression of homologous recombination genes, cell proliferation and cell damage. BMI‐1 was silenced through lipofectamine‐based siRNA (Invitrogen). We accessed gene expression through Real‐Time PCR reactions in MCF‐7 cell line. Cells were subjected to MTT assay for determination of proliferation rate. Immunofluorescence was also performed to access BMI‐1 and γH2AX (DNA damage marker) protein expression. BMI‐1 silenced cells proliferated significantly less than control (p<0.001). BMI‐1 silencing significantly reduced ATM (p<0.001), ATR (p<0.001), BRCA‐1 (p=0.001), BRCA‐2 (p<0.001), H2AX (p=0.001), TP53 (p<0.001), RAD51 (p<0.001) and TOP3β (p=0.037) expression. Immunofluorescence staining showed that cells positive for BMI‐1 were also positive for γH2AX, while silenced BMI1 cells had reduced expression of γH2AX (nuclear staining). Our results showed that BMI‐1 positive cells may have a more aggressive behavior in breast cancer.Grant Funding Source: Supported by: FAPESP (2011/23845‐2)