The purpose of this study was to evaluate the effect of resveratrol on cytogenetic damages of iododeoxyuridine (IUdR) and x-ray megavoltage radiation (6 MV) in spheroid model of U87MG glioblastoma cancer cell line using clonogenic and alkaline comet assay. Cells were cultured as spheroids (350 µm) that were treated with 20 μM resveratrol, 1 μM IUdR and 2 Gy of 6 MV x-ray. After treatment, viability of the cells, colony forming ability and the induced DNA damages were examined using trypan blue dye exclusion, colonogenic and alkaline comet assay, respectively. Our results showed that resveratrol could significantly reduce the colony number and induce the DNA damages of the cells treated with IUdR in combination with 6 MV x-ray radiation. That results indicated that resveratrol as an inhibitor of hypoxia inducible factor 1 alpha (HIF-1α) protein in combination with IUdR as a radiosensitizer enhanced the radiosensitization of glioblastoma spheroid cells.