MgO nanoparticle was synthesized by sol-gel method from magnesium acetate and oxalic acid dissolved in methanol followed by annealed process. Characterization of functional groups was performed using (FTIR) Fourier Transforms Infrared spectroscopy, crystal profile analysis using (XRD) X-ray Diffraction and morphology using (SEM) Scanning Electron Microscopy. The FTIR and XRD results indicated that the magnesium acetate converted into magnesium oxalate (Precursor), and then the anneal process was changed into MgO nanoparticles. The Scherrer's equation used to determine the distribution of MgO nanoparticle crystals. Modified Williamson-Hall plot is used to determine the strain, stress and energy density value (micro structural properties) based on angle values 2θ and (FWHM) Full width at half maximum of XRD angles from 10° to 80°. The results of the XRD and SEM analysis show that magnesium complexes have changed. The solid layer formed by the Mg polymer complex network is transformed into a cubic structure.