Zinc oxide-nanoparticles (ZnONPs)–reduced graphene oxide (rGO) composites with a high degree of crystallinity and a high dispersity were successfully synthesized via a one-pot, facile sol–gel method in a starch environment, during which the formation of zinc oxide nanoparticles, the reduction of graphene oxide and the loading of the ZnONPs onto the rGO surface occur simultaneously. Starch, as a natural capping agent, plays a significant role in controlling the degree of dispersion and coverage of the ZnONPs. The effect of rGO on the crystalline structure and optical properties of the ZnONPs was determined via X-ray diffraction, UV-visible diffused reflectance spectroscopy and photoluminescence spectroscopy. The ZnONPs+rGO composites exhibit excellent potential for photocurrent generation compared with pure ZnONPs under visible light irradiation, provided that efficient photo-induced charge separation and transportation can be achieved at the interface. The maximum photocurrent response, crystalline quality and factor optical properties (NBE/DLE ratio) were obtained for the ZnONPs+rGO composite with a 1.7% mass fraction of rGO, which is twice that achieved on pure ZnONPs.