By a facile solid-state reaction method with urea as a nitrogen source, HNb3O8 could be successfully doped with nitrogen without destroying its layered structure. It was found that the intercalation of urea not only helps to stabilize the layered structure of HNb3O8 during the heating process, but also facilitates an easier doping of nitrogen into the solid acid. The nitrogen-doped HNb3O8 photocatalyst so-obtained shows fairly good activity under visible light irradiation.