NO adsorption on differently pretreated pure TiO2 and Ru/TiO2 samples has been investigated using FTIR spectroscopy. The analysis of the IR spectra concerns both the variations of the IR transparency, related to the electronic properties of the samples, and the vibrational modes of the adsorbed species. The experimental results are discussed taking into account the reducibility of the titania and the effect of the different valence states of Ru on the electronic and chemical behavior of this system.