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Graphene‐Fe3O4(G‐Fe3O4) composites were prepared with a solvothermal method for the immobilization of horseradish peroxidase (HRP) to construct a mediator‐free H2O2biosensor. The morphology and structure of the G‐Fe3O4composites were analyzed by TEM, SEM, and XRD. Chitosan (CH) was utilized to disperse the composites, and the mixture of CH, G‐Fe3O4and HRP was spin‐coated on an indium tin oxide (ITO) electrode to form a biocomposites film. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) demonstrated the fast electron transfer process between HRP and the electrode. The resulted H2O2biosensor exhibited a rapid response upon the addition of H2O2, a high sensitivity of 132 µA mM−1cm−2and a low detection limit of 6×10−7M. The linear range of the biosensor is from 5×10−6to 3.81×10−3M (r=0.997). Such interesting G‐Fe3O4composites with easy preparation and low cost can provide a novel matrix for enzyme immobilization to construct biosensors with higher performance.