Introduction: Glioblastoma is one of the most common and a dangerous cancer of central nervous system.Targeted radiotherapy is an effective method in its treatment. IUdR is -a thymine analog- known as a radiation sensitizer in cancer therapy. It has been reported that Methoxyamine increase base cutting healing blocking in DNA damages levels in cells derived from human Glioblastoma, while the degree of DNA fractures in larger spheroids were decreased, this matter was affected by increasing in IUdR uptake by harvested cells in G0 phase is. HIF-la is a transcription factor for endothelial cells stop cell cycle phase G 0 / G 1. Recently has been recognized that activity by HIF-1a can be cause 2 - Methoxyestradiol inhibited, this issue that is leads to inhibition of cell cycle stopping.Material and Methods: In this studywe have investigatedcombinedingeffect 2 - Methoxyestradiolon radio sensitivity consideration of IUdR in Spheroid cell culture model Glioblastoma. U87MG cells cytotoxic damages were tested by colony assay and the colonogenic ability of cells were evaluated and compared in 350 microns spheroieds.Result: Our results shown that the damage resulted by ionizing radiation before yielding in IUdR treated with estradiol and Methoxyamine much more (001 / 0³p) of the use each of these factors alone are.Conclusion: These results were indicated the important role of methoxyestradiol in related by IUdR in cancertherapy.