In order to investigate mechanisms of ATM (Ataxia telangiectasia mutated) genes mediating phosphorylation of BRCA1(breast cancer gene 1) and its downstream gene RAD51 (DNA damage repair protein 51) in signaling pathway of DNA injury repair, we applied immunocoprecipitate and Western blot to observe changes in the expressions of BRCA1 and RAD51 proteins in AT cells, ATM,+,-AT cells (AT cells transfected with ATM genes) and GM cells (originated from human skin fibroblast, GM 0639) and used as control, after 5, 10 and 20Gy ,60,Co γ-ray irradiation at dose rate of 1.0Gy/min. The irradiated AT cells were analyzed to study interactive action between ATM and BRCA1 protein, BRCA1 and RAD51 protein, and the effect of PI3K inhibitor on ATM phosphorylating, its downstream gene, by immunocoprecipitate and Western blot. No expression bands of BRCA1 were found in ATM,+,-AT and GM cells of the control. After the irradiation, the BRCA1 and RAD51 were both expressed in GM and ATM cells. The PI3K inhibitor Wortmannin could inhibit the expression of BRCA1 in the AT, ATM,+,-AT and GM cells. The BRCA1 and RAD proteins were both expressed in ATM,+,-AT cells and GM cells. Therefore, after the irradiation the phosphorylation of BRCA1 mediated by ATM could further interact with RAD51. This is a cascade in signaling pathway for DNA damage repair and genome stabilization.