In this study the magnesium oxide nanoparticles were synthesized via the sol-gel method and annealed at different temperatures between 400 and 800 degrees C in air. In order to evaluate the microstructure of samples, the scanning electron microscopy technique as well as the advanced X-ray diffraction analysis (DIFFaX software and eCMWP fitting procedure) was used and the behavior of crystallite size, size distribution function, dislocation density, the fractions of edge/screw dislocation characters and the probability of planar defects were studied as a function of annealing temperature. (C) 2014 Elsevier B.V. All rights reserved.