ZnO/reduced graphene oxide (RGO) composites were prepared in-situ by solution combustion method using zinc nitrate and graphene oxide as oxidants and mixture of glycine and citric acid as fuel in the absence of air oxygen (closed system). Reduction of graphene oxide during combustion reaction was confirmed by the appearance of D and G bands in Raman spectra, in spite of the absence of its reflection in X-ray diffraction patterns. Scanning and transmission electron microstructure revealed the uniform distribution of ZnO nanoparticles on RGO sheets. With the addition of RGO, the light absorption increased in the visible region and band gap energy decreased from 3.21 to 3.14 eV in comparison with ZnO powders. About 98% of methylene blue (MB) was photodegraded in the presence of ZnO/RGO composite prepared by using 20 wt. % of graphene oxide, while pure ZnO powder photodegraded 82% of MB during 2 h UV irradiation.