Porous nanocrystalline ZnGa2O4 catalysts were synthesized by a simple soft-chemical method at low temperature. The catalysts were characterized by XRD, nitrogen adsorption, SEM, TEM, UV/ vis, and FT-IR spectroscopy. The activity of the photocatalysts was evaluated by decomposition of benzene and its derivatives in the gas phase. It was found that hydrothermal treatment resulted in the formation of spinel ZnGa2O4 with a large surface area of 43-201 m2 x g(-1) depending on the synthetic temperature. The optimum synthetic temperature was found to be 80 degrees C, at which the sample possessed a surface area of 201 m2 x g(-1) and had the highest photocatalytic activity for degrading benzene. A comparison with TiO2 and Pt/TiO2 showed that the ZnGa2O4 (synthesized at 80 degrees C) had improved photocatalytic activity and durability over the TiO2-based catalysts. No remarkable deactivation of the ZnGa2O4 catalyst was observed in 80 h photoreaction, whereas the TiO2 deactivated remarkably in 24 h reaction. The high photocatalytic performance of porous ZnGa2O4 catalysts can be explained by the large specific surface area, the accessible porous framework, and the high redox power.