MgO prepared with the sol-gel technique had crystalline structure defects, obtained from X-ray powder diffraction and crystalline structure refinement, that correlated with its acidic and basic sites, The acidic sites, measured by adsorbing pyridine and NH3, were found when brucite and MgO coexisted, which only occurred after annealing the sample at 673 K, Two different basic sites, measured by adsorbing CO2, were present in a total concentration of about 10(21) sites per gram. These sites correlated to the presence of magnesium vacancies in MgO crystal. Both basic site and magnesium vacancy concentrations diminished when the sample annealing temperature was increased.