A series of nitrogen-doped TiO
2 nanocatalysts have been synthesized successfully by a two-step hydrolysis-calcination method in which condensed HNO
3 (~16 mol/L) was first used. In contrast to the traditionalhydrolysis method, the time consumed in the hydrolysis process was shortened greatly. The content of nitrogendecreases as the calcination temperature increases, resulting in the variation of bandgaps of the as-synthesizedN-doped TiO
2 from 1.55 to 2.95 eV. Decomposition of methylene blue under visible light irradiation (
400 nm) has been carried out to evaluate the photocatalytic activity of the as-synthesized N-doped nanocatalysts.Compared to P25, greatly improved photocatalytic activity for water contaminant decomposition under visiblelight irradiation was obtained due to the doping of nitrogen into the titania system. The crystallinity of thephotocatalysts was found to be less influential than the nitrogen content in determining the photocatalyticactivity.