Abstract: Objective 　This study was designed to determine the relationship between expression of DNA-PKcs gene (a catalytic subunit of DNA-PK,which is an important component in NHEJ pathway) and radiosensitivity of nasopharyngeal carcinoma cell lines. Methods 　Radiosensitivity parameters of nasophryngeal carcinoma cell lines were obtained by the colony forming assay and irradiation dose-survival curve were done by linear quadratic model. The two cell lines were exposed to ⁶⁰ Co-γ ray and received 4 Gy, 12 hours later, the survival rate were obtained by MTT assay, and evaluated the different radiosensitivity of two cell lines. After receiving different irradiation dose, the dynamical changes of the expression of DNA-PKcs in mRNA level of CNE-1 and CNE-2 were detected by RT-FQ-PCR. Results 　Survival rate of CNE-1 was higher than those of CNE-2 at each dose point . Mean inactivation dose was higher in CNE-1 (2. 78) than that in the CNE-2 (1. 61), and the SF₂ was 0. 627 and 0. 341 respectively. After exposed to irradiation dose of 4 Gy, survival rate in CNE-1 was also higher than that in the CNE-2. The ratio of relative expression of DNA-PKcs in the two cell lines was 7. 54 ±2. 71 ( t = 4. 17, P = 0. 014) . The expression of DNA-PKcs in CNE-2 was correlated with the irradiation dose and postirradiation time. Conclusion 　CNE-2 is more radiosensitive than CNE-1. The expression of DNA-PKcs gene is correlated with the radiosensitivity of nasophryngeal carcinoma.