Abstract: Objective: To analyze the radiosensitization effect of gemcitabine in human nasopharyngeal carcinoma cell line CNE-2 in vitro. Methods: Flowcytometry was used to observe the effect on cell-cycle of γ-irradiation in conjunction with gemcitabine on CNE-2 cells. Results: Irradiation resulted in G₁ block in a dose-dependent (<6 Gy) manner. Concentrations of 5 mg/L, 10 mg/L, or 15 mg/L gemcitabine were incubated with CNE-2 cells for 24h prior to irradiation with 2 Gy, resulting in significant S-phase block. G₁ block was observed following increased doses of irradiation. 15nmol/L gemcitabine was incubated with CNE-2 for 12h prior to 2 Gy irradiation, resulting in an immediate G₁ block that switched to an S-phase block after 24h and that lasted for at least 36 h. Conclusion: Radiosensitization of gemcitabine in CNE-2 cells is associated with induction of S-phase and /or G₁ block.