A renewable electrochemical immunosensor was developed for the determination of transferrin in human serum. It is based on a paraffin-graphite-transferrin antiserum biocomposite, which needs no additional curing. A competitive binding assay was used to determine transferrin in human serum with the aid of transferrin labeled with horseradish peroxidase. The assay conditions were optimized, including the loading of transferrin antiserum in the biocomposite, the amount of labeled transferrin in the incubation solution, incubation time and temperature. Serum samples were analyzed and the results demonstrate that the concentration range of determination with this system meets the demands of clinical analysis. The surface of the immunosensor can be regenerated by simply polishing to obtain a fresh immunocomposite ready to be used in a new competitive assay.