Sonochemical synthesis followed by supercritical drying was used to prepare MgO nanoparticles from Mg(OCH 3 ) 2 and Mg(OC 2 H 5 ) 2 . Their physicochemical properties were examined by means of X-ray diffraction (XRD), simultaneous thermal analysis (DTA, TG, EGA), specific surface area measurement, scanning and transmission electron microscopy. The dehydrated MgO oxides were free of -OCH 3 groups. The highest values of specific surface area (1236 m 2 g - 1 ) have been obtained by hydrolysis of magnesium methoxide using toluene as solvent agent.