Nanosized powders exhibit high specific surface areas resulting in enhanced reactivities. Surface tailoring by controlled adsorption of molecules can thus be conveniently performed and more easily monitored by surface-sensitive techniques. In situ and ex situ grafting procedures of hexamethyldisilazane (HMDS) on nanosized titania (n-TiO2) powder were carried out and studied by Fourier transform infrared spectrometry (FT-IR). In addition to a decrease of the hydrophilic OH groups, the vibration analysis revealed hydrophobic CH3 groups on the grafted samples. Co-adsorption of CO and H2O on the differently grafted samples showed a large reduction of water effect compared to the as-received n-TiO2 powder. Modulation of infrared transmitted energy by controlled adsorption of O2 and CO made it possible to qualitatively compare the electronic properties of the surface-tailored samples.