C, N co-modified niobium pentoxide (Nb₂O₅) nanoneedles have been successfully synthesized via a facile hydrothermal method with Niobium Chloride (NbCl₅) as a precursor and triethylamine as both the carbon and nitrogen source. The formation process of Nb₂O₅ nanoneedles has been presented in detail by investigating the effect of the crystallization temperature, the amount of triethylamine and the calcination temperature. The as-prepared Nb₂O₅ nanoneedles exhibit more efficient photocatalytic activity than commercial Degussa P25 and commercial Nb₂O₅ towards photodegradation of Rhodamine B (RhB) at a concentration of 10 mg L⁻¹ under visible light. Special chemical species, such as carbonate species and NO_X species, that exist on the surface of the as-prepared catalyst could extend the absorption into the visible region and thus enhance the photocatalytic activity of the Nb₂O₅ nanoneedles. At the same time, the obtained Nb₂O₅ nanoneedles exhibit excellent stability even after three successive cycles. A possible photodegradation mechanism was proposed and the corresponding photodecomposition process of RhB over the Nb₂O₅ nanoneedles was elucidated by a reactive species trapping experiment, suggesting that h⁺ and O₂˙⁻ play a major role in the photodegradation of RhB in aqueous solution.