[en] In this research, the influence of γ-irradiation on the optical and structural properties of magnesium oxide (MgO) nanoparticles was studied. The MgO nanoparticles were irradiated with doses 100 Gy, 1 kGy, 10 kGy and 20 kGy from ${}^{60}$Co source. The as-synthesized samples of MgO nanoparticles prepared by the sol-gel technique were analyzed by XRD which suggested the double phase; cubic and hexagonal structures of the material. The crystal defects that produced in the cubic and hexagonal lattice were studied before and after ${}^{60}$Co γ-irradiation in a gamma cell by different dose rates in order to report the changes in structural properties of the MgO nanoparticles. The irradiated and un-irradiated samples were characterized by XRD and UV–Vis. The XRD pattern of MgO nanoparticles is showed that the crystal size of MgO nanoparticles being increased with increasing the γ-ray dose rate. For optical absorption, the UV–Visible absorption spectra of MgO nanoparticles are showed that when the dose rate is increased, the value of band gap is decreased. Also, the experimental values of the mass attenuation coefficient of MgO nanoparticles have been calculated before and after γ-irradiation by using the gamma spectroscopy method. Therefore, the results are showed that γ-ray irradiation has various effects on structural, morphological and optical properties.