To explore the effect of Ku70 on breast cancer susceptibility genes BRCA1 after irradiation, the BRCA1 protein and its mRNA expression after transfecting into tumor cells with siKu70 or Ku70 plasmid DNA, and the impact of Ku70 on BRCA1 expression in SGC7901, EC109 and H460 cell lines were investigated after irradiation. The results indicate that both protein and transcription of BRCA1 were obviously reduced in tumor cell lines after pretreated with siKu70, and siKu70 can reduce radiation-induced BRCA1. Similarly, after transfection of Ku70 plasmid DNA, expression of BRCA1 was higher than that of the control group meanwhile there was a significant increment of BRCA1 in irradiation group compared with that of no irradiated group. The results suggest that Ku70 gene might be relative to BRCA1 expression, and it might be involved in radiation-induced BRCA1 at transcriptional level.Cited