In this paper, we present a simple method for preparation of graphene-ZnO nanocomposites (G-ZnO). The method is based on thermal treatment of the graphene oxide (GO)/ZnO paste which reduces the graphene oxide into the graphene and leads to the formation of the G-ZnO nanocomposite. The structure, morphology and optical properties of synthesized nanocomposites are characterized with XRD, FESEM, FTIR and Raman spectroscopies. Here CdS quantum dots are deposited on G-ZnO nanocomposite structure and is integrated as a photoanode in CdS quantum dot sensitized solar cells (QDSSCs). Photovoltaic properties of CdS QDSSC based on bare ZnO nanoparticles and G-ZnO nanocomposite photoanodes are studied here. The cell with G-ZnO/CdS photoanode shows two times higher photoelectric conversion efficiency than that of the pure ZnO photoanode (0.94 vs. 0.45).