[en] Objective: To study the effect of the specific inhibitor Wortmannin(WT)on repair of radiation damage of thymocyte DNA in mice. Method: The cells were exposed to WT or DMSO(solvent) for 1 h, and then irradiated at the indicated doses. After indicated times post irradiation, the cells were washed to remove the WT, their DNA was made out, then DNA damage and repair were detected by electrophoresis. Results: After 10 Gy and 20 Gy γ-irradiation, dsb level was higher in WT group than in control group. It was more evident at 1-3 hrs after irradiation. Conclusion: The radiosensitizing effect of WT is related to its inhibition of dsb repair after irradiation