In this study, knockdown of Tip60 could enhance the sensitivity of prostate cancer cells to X‐ray irradiation by inducing apoptosis, confirmed by the expression pattern change of Bcl‐2, cleaved caspase 3 and cytochrome C. In addition, we also found depletion of Tip60 significantly reduced the acetylation of ATM after X‐ray irradiation and a further study demonstrated the phosphorylation levels of molecules downstream of ATM, including Chk2, and cdc25A, were decreased after Tip60 knockdown. This evidence concerns the gene CASP3 and prostate cancer.