Graphene/ZnO nanocomposites have been synthesized using hydrothermal method at two different temperatures 80 and 90 degrees C. The structure, morphology and optical properties of as synthesized nanocomposites were analyzed through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM) and UV-vis absorbance spectroscopy. The XRD pattern confirmed the formation of graphene decorated by hexagonal ZnO with high crystallinity. FESEM image revealed that the sheet like graphene decorated with ZnO in homogeneously. Decoration of quasi-spherical ZnO nanoparticles on graphene sheet was confirmed by TEM. The characteristic absorbance peaks of graphene/ZnO nanocomposites were observed in UV visible spectra. The photocatalytic degradation experiment was performed against rhodamine-B dye and showed good catalytic activity for both samples. The graphene/ZnO nanocomposites showed higher catalytic activity then ZnO nanoparticles. The GZN-90 sample showed more catalytic activity than GZN-80 due to higher density of ZnO in graphene surface generates large number of photo-induced electron. (C) 2012 Elsevier Ltd. All rights reserved.