Graphite oxide was prepared by Hummers method and treated by ultrasonic waves to obtain graphene oxide. CdS–graphene composites were successfully synthesized via a one-step solvothermal method with different Cd/S ratios, with cadmium acetate as cadmium source, thiourea as sulfur source and ethylene glycol as reaction solvent and characterized by X-ray diffraction, scanning electron microscopy and UV–vis absorption spectra. The photoelectric characteristics of CdS–graphene composites were evaluated by transient photocurrent response and three-electrode cyclic voltammetry.