DFT study on O-2 adsorption on a nanocrystalline titania is presented for the first time. The dioxide's nanoparticle is modeled via the nanocluster Ti8O16. According to the calculations, O-2 physisorbs on the nanocluster Ti8O16 in S-0 and T-0 states and chemisorbs on the nanocluster in S-1 state. The computed adsorption enthalpies, O-2 vibrational frequencies, and O-2 g-tensor agree well with available data. In contrast to the axial O-2 orientation on a surface of titania with oxygen vacancies, in the chemisorption complex O-2 is oriented laterally. We explain this by the sterical hindrance of the Ti3+ centers in the former case. (C) 2018 Elsevier B.V. All rights reserved.