Oxygen adsorptions on anatase surfaces and edges are investigated with semi-empirical method MSINDO. After adsorption, an O-2(-) forms on (1 0 1) and (1 0 0) surfaces and facets related edges, while a Ti-O-O-O-Ti bridge forms on the (0 0 1) surface or (0 0 1) surface related edges. Electrons transfer from the anatase to the adsorbed oxygen molecules which can be used to hinder the electron hole recombination during the photo-catalytic processes. Oxygen adsorption on (0 0 1) surfaces and (0 0 1) facets related edges are more energetic favorable than the adsorption on (1 0 1) and (1 0 0) facets or related edges. For the adsorptions on (1 0 1), (1 0 0) surfaces and the edges related with those two facets, edge adsorptions are more energetic favorable than the surface adsorptions. We do not see this edge effect on the (0 0 1) surface. Small size particles with more edges or particles with more (0 0 1) facets can adsorb more oxygen molecules and hinder the electron hole recombination more efficiently, and those adsorbed oxygen molecules may also oxidize other absorbed small toxic gas molecules. (C) 2011 Elsevier B. V. All rights reserved.