ZnGa2O4 nanoparticles (NPs) have been successfully anchored onto reduced graphene oxide (RGO) nanosheets by a self-assembly approach under facile solvothermal condition. The as-synthesized ZnGa2O4-RGO nanocomposites were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The results reveal that ZnGa2O4 NPs with a well-controlled size and uniform distribution were successfully assembled onto RGO sheets. Moreover, both methylene blue (MB) and rhodamine B (RhB) were employed as model pollutants to evaluate the ability of as-prepared ZnGa2O4-RGO nanocomposites for wastewater treatment. The content of RGO sheets was found to be crucial for optimizing the photocatalytic activity of various nanocomposites with a key value of 5% beyond which the adsorption ability of ZnGa2O4-RGO nanocomposites for dyes dominates the process of water treatment. (C) 2014 Elsevier Ltd. All rights reserved.