It is reported for the first time that horseradish peroxidase (HRP) immobilized on the active carbon can undergo a direct quasi-reversible electrochemical reaction. In addition, the immobilized HRP showed the stable bioelectrocatalytic activity for the reduction of H2O2. It is reported for the first time that horseradish peroxidase (HRP) immobilized on the active carbon can undergo a direct quasi-reversible electrochemical reaction. In addition, the immobilized HRP showed the stable bioelectrocatalytic activity for the reduction of H2O2.