Abstract: Objective To investigate the radiosensitivity enhancement of nano Fe3O4／CD133Ab complex on human brain glioma U251 cells. Methods Immunohistochemical staining was used to detect the expression of CD133 molecules in human glioma U251 cells.U251-CD133+cells were isolated by FACS.The toxicity of nano Fe3O4／CD133Ab complex and CD133Ab were determined by MTT. Colony-forming assay was employed to observe the effects of nano Fe3O4／CD133Ab complex and CD133Ab on the radiosensitivity of the human brain glioma U251 cells. Results The positive expression of CD133 molecules was observed in human glioma U251 cells, and CD133-positive cells were selected. The proliferation inhibition rate of human glioma U251 cells and U251-CD133+cells gradually increased with the increasing concentration of nano Fe3O4／CD133Ab complex in 0.0488-25μg／ml range in a significant dose-effect manner. The maximum of tumor cell proliferation rate was 59.46％ and 56.66％. The IC50 was 11.84μg／ml and 12.06μg／ml. The proliferation rate between nano Fe3O4/CD133Ab complex + radiotherapy and CD133Ab+ radiotherapy was of statistic significance（P＜0.05）. And when the X-ray doses were greater than 4Gy，the effects were enhanced with the increasing doses.Conclusion The nano Fe3O4／CD133Ab complex has toxicity on the human glioma U251 and U251-CD133+cells. It also has radiosensitizing effects on U251-cells.