Objective: To study the effect of coixenolide (CXL) on irradiation of human nasopharyngeal carcinoma cell line CNE-2Z in the absence of oxygen. Methods: Microcolony formation assay was used for determining the sensitivity of CNE-2Z to γ-ray in vitro. Results: When CNE-2Z was treated with 10^-7 ~ 10^-6 mol/L of CXL, CXL shifted the radiation dose-survival curve to the left, with the decrease of D₀, D_q and N values. Radiation dose reduced 10.07%~35.69% at D37 level, the sensitizing enhancement ratios (SER) were 1.07~1.43 and 1.16~1.72 at D₀ and D_q levels respectively. Conclusion: CXL increase susceptibility of CNE-2Z to ray under hypoxic condition by the mechanism of inhibiting its sublethal damage repair. Subject words Nasopharyngeal neoplasm; Coixenolide; Radiosensitization, Hypoxic irradiation