Abstract: Titanium dioxide (TiO₂) nanopowder (P-25; Degussa AG) was treated using dielectric barrier discharge (DBD) in a rotary electrode DBD (RE-DBD) reactor. Its electrical and optical characteristics were investigated during RE-DBD generation. The treated TiO₂ nanopowder properties and structures were analyzed using x-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). After RE-DBD treatment, XRD measurements indicated that the anatase peak theta positions shifted from 25.3° to 25.1°, which can be attributed to the substitution of new functional groups in the TiO₂ lattice. The FTIR results show that hydroxyl groups (OH) at 3400 cm⁻¹ increased considerably. The mechanism used to modify the TiO₂ nanopowder surface by air DBD treatment was confirmed from optical emission spectrum measurements. Reactive species, such as OH radical, ozone and atomic oxygen can play key roles in hydroxyl formation on the TiO₂ nanopowder surface.