A new biomaterial containing covalently bound hyaluronidase was prepared. An application of this enzyme membrane is to improve the performance of an implantable fuel cell. Hyaluronic acid is a contributor to the viscosity of tissue fluids but can be a potential fuel source because of its sugar content. The incorporation of immobilized hyaluronidase would not only contribute to a more available fuel supply by splitting hyaluronic acid but, perhaps more importantly, enhance the rate of mass transport of fuel, O2, and reaction products by reducing the viscosity near the electrode membranes. Hyaluronidase was bound to Sepharose gel and its thermoplastic membrane after activation by cyanogen bromide. Fourteen and 22% of the activities were recovered from the gel and membrane, respectively. The activity of the bound enzyme was stable for six months at 0°C. The addition of hyaluronic acid, 1 mg/ml, to a typical implantable type bioautofuel cell in vitro increased external solution viscosity from 1.1 to 2.5–2.8 cP and reduced voltage output under 10 kΩ by 60% in 3 hr. When the hyaluronidase bound membrane was placed at the anode, viscosity of the glucose–hyaluronic acid solution was lowered to 1.8 cP and the cell output increased to the original level of a glucose‐fueled cell in 3 hr. Glucosamine‐equivalent released from hyaluronic acid at the electrode was 3.1 mg after 22.5 hr. This represents 90% of the theoretical consumption. Restoration of the cell output was probably a combination of the enhanced transport of fuel, O2 and products, and/or appearance of a new fuel, glucosamine‐equivalent.