Abstract: Objective To identificate a novel transcriptional coactivator of AP-2α and explore new therapeutic target for AP-2α overexpressed breast cancers. Methods AP-2α,as a bait,and its interactive proteins were detected by yeast two-hybrid technique. The interaction between AP-2α and its interacting partner was verified by co-immunoprecipitation assay. The subcellular colocalization of AP-2α and its interacting partner was detected by immunofluorescence technique. Luciferase assay was performed to characterize the effect of AP-2α-interacting protein on the transcriptional activity of AP-2α. Results Ku70 was identified as a novel interactive protein of AP-2α by yeast two-hybrid technique. The interaction between AP-2α and Ku70 in cells was verified by co-immunoprecipitation assay. Furthermore, both AP-2α and Ku70 are colocalized in nucleus. Functionally we found that Ku70 can increase transcriptional activity of AP-2α. Conclusion This study for the first time reveals that Ku70 can bind with AP-2α and enhance its transcriptional activity. Our results demonstrate that Ku70 is a novel transcriptional coactivator of AP-2α and suggest that Ku70 is a potential new therapeutic target for AP-2α overexpressed breast cancers.