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 cm1 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.