The grain boundaries in nanocrystalline MgO were formed by dehydration of densified magnesium hydroxide aerogel. Its configuration was regulated by controlling the contact interface between the nanocrystals in the hydroxide precursor. The materials with high contact interface were obtained by application of chemical (multiple aerogel condensation) and physical (pressing) densification methods. Formation of distorted zones at the grain boundaries areas in the MgO densification process increased its surface basicity by as much as 8 times at a crystal domain size of 5 nm. The grain boundaries contribution to the creation of coordinative unsaturated surface ions and vacancies in nanocrystalline MgO was determined by a variety of physical and chemical methods. The significant increase of surface basicity yielded a major enhancement of catalytic activity of densified MgO material measured in Knoevenagel condensation of benzaldehyde with malononitrile and transesterification of phenyl acetate with I-phenylethanol. (C) 2009 Elsevier Inc. All rights reserved.