A simple method for the doping of titanium dioxide with nitrogen was developed. By this technique, commercial titanium dioxide was thermally treated under a nitrogen enriched atmosphere. The N doped TiO₂ presented a slight displacement in the absorption edge of light, towards the visible radiation range. Phenol degradation in water solution was used to compare photocatalytic activity of doped titania. With the treatment at 600°C, the photocatalitic activity of the N–TiO₂ was improved, and the changes of anatase to rutile phases ratio as well as specific surface area were minimal. The higher activity obtained after TiO₂ treatment could be correlated with the modification in radiation absorption spectra, since the radiation used for the determination of the photocatalytic activity was in the edge of the UV–vis radiation. Treatments at higher temperature shown almost the same activity of undoped titania, but sintering reduced the surface area per gram of TiO₂, thus the photocatalytic activity of doped surface was more active (moles of phenol transformed/m²h).