Abstract: Ionizing radiation can cause double strand break (DSB), Ku protein as a heterologous dimmer; mainly join in non-homologous end-joining repair pathway. Ku protein plays a crucial role in maintaining telomere structure. There is an abnormal expression of Ku protein in human different tumors. The expression and function of Ku protein is relate to resistance of tumor radiotherapy and chemotherapy. Inhibition of Ku protein can enhance the sensitivity of radiotherapy and chemotherapy. Therefore, Ku protein can be used as target of enhancement of radiotherapy and chemotherapy.