The photocatalytic degradation of nitrobenzene and substituted nitrobenzenes under UV exposure was investigated with combustion synthesized nano-TiO2 and commercial TiO2 catalyst, Degussa P-25. The experimental data indicated that the photodegradation kinetics was first order. The photocatalytic degradation rates were considerably higher when catalyzed with combustion synthesized TiO2 compared to that of Degussa P-25. The degradation rate coefficients followed the order: 1-chloro,2,4-dinitrobenzene≃4-nitrophenol>2-nitrophenol> 1-chloro,4-nitrobenzene>3-nitrophenol>2,4-dinitrophenol> 1-chloro,2-nitrobenzene>nitrobenzene>1,3-dinitrobenzene. Plausible mechanisms and reasons for the observation of the above order are discussed. © 2005 Elsevier B.V. All rights reserved.