Functionalized graphene/ZnO (FGZnO) nanohybrids with strong chemical coupling and electronic interaction were synthesized through a modified in situ synthesis method by combining two procedures: functionalization of graphene oxides and solution-based synthesis of FGZnO. ZnO species with morphologies of nanorods or nanoplates were densely attached on the graphene sheets. The effectiveness of this method for loading ZnO onto graphene with good interface contact was confirmed by using scanning electron microscopy, transmission electron microscopy, XPS measurements, and UV-Vis spectroscopy. Gas sensors based on the nanohybrids have faster response, higher sensitivity, and better selectivity to ethanol compared with pure ZnO nanorods. The mechanisms to interpret the formation of nanohybrids and their enhanced gas-sensing performance were put forward.