The correlations between microstructure of nanocrystalline TCO SnO2 and In2O3 and parameters of oxygen chemisorption are analyzed. Nanocrystalline SnO2 and In2O3 were prepared by wet chemical method. The sample's microstructure was characterized by TEM, XRD and low-temperature nitrogen adsorption. Electrical properties of TCO were studied at 200-400 degrees C depending on the oxygen partial pressure. increase of TCO grain size leads to the increase of the fraction of atomic forms of chemisorbed oxygen at the fixed temperature. It could be due to the decrease of surface barrier resulting in the decrease of activation energy of dissociation of molecular ion O-2(ads)(-). (C) 2009 Elsevier B.V. All rights reserved.