Titanium dioxide (TiO2) is one of the most important materials with many applications in both fundamental science and technology. Among various forms of TiO2 nanostructures, clusters are the most widely used due to high surface to volume ratio. In this context, we present first principles calculations to study the size-dependent evolution of the chemical reactivity and site selectivity of (TiO2)(n) nanoclusters with n = 5-10. In the framework of the density functional theory, we employ the global parameters to quantitatively describe the chemical reactivity of different sizes of (TiO2)(n) clusters. Then, on the basis of the symmetry for each size of TiO2 cluster, susceptibility of Ti and O atoms pertinent to nucleophilic and electrophilic attacks is anticipated using local reactivity descriptors. Further, we validate the obtained reactivity pattern for considered (TiO2)(n) clusters by explicit adsorption of H2O2. It is found that upon the adsorption, H2O2 decomposes to two OH radicals that are stabilized by the interaction with Ti and O atoms on the cluster surface. The characterization of Ti center dot center dot center dot O and O center dot center dot center dot H interactions has also been performed by analyzing the parameters derived from the quantum theory of atoms in molecules. (C) 2016 Elsevier B.V. All rights reserved.