ZnGa2O4 nanoparticles are obtained by microwave-hydrothermal method through homogeneous coprecipitation reaction using urea as precipitant with surfactant assembly. Synthetic temperature, surfactant, and calcination temperature have the obvious effect on the formation and photocatalytic activity of ZnGa2O4. ZnGa2O4 nanoparticles synthesized in the optimal conditions are highly dispersed and uniform with average diameter of 16.2nm possessing a surface area of 70m2g−1. Under ultraviolet (UV) light illumination, the ZnGa2O4 nanoparticles show an efficient photocatalytic activity in liquid phase degradation of organic dyes. The decomposition rates of methyl orange and methylene blue over the present ZnGa2O4 nanoparticles are higher than those of commercial P25 (Degussa Co).