Metal nanoclusters deposited on oxides as support play an important role for the design of catalysts model with applications in heterogeneous catalysis. In general, the oxide contributes to stabilize the nanoparticles avoiding their sintering. Noble metals such as silver (Ag) supported on reducible oxides such as titania have been shown to be efficient for the reduction of harmful gases such as nitrogen oxides (NOx). In order to improve the performance of the catalyst and the fundamental knowledge of the nature of the catalytic activity, it was decided to study the titania as support for this system. From ab initio calculations using the Density Functional Theory (DFT + U), the energetic and structural properties of Ag-4 clusters were studied in tetrahedral and planar configurations deposited on the stoichiometric surfaces of ruffle TiO2(110) and anatase TiO2(101) to characterize the different aspects of the metal-oxide interaction that provide valuable information for future research. For both surfaces, we find that the tetrahedral configuration is preferred, as experiments indicate. In all cases studied, the Ag nanoparticles are oxidized, yielding its electrons to the titania. The highest net charge transfer occurs in the case of the ruffle surface and is related to the highest adsorption energies observed. However in the case of anatase surface a reversal in the relationship is observed: higher charge transfer, lower adsorption energy.