An IgG immunosensor using a colloidal gold‐Tyrosinase‐graphite‐Teflon composite biosensor as an amperometric transducer is reported. Protein A was used to immobilize the antibody on the biosensor surface and a sandwich‐type configuration using alkaline phosphatase (AP) labeled anti‐IgG was employed. Phenyl phosphate was used as the AP‐substrate, and the enzyme reaction product, phenol, was catalytically oxidized by tyrosinase to the o‐quinone, which is subsequently reduced at −0.1 V at the biocomposite electrode. Variables such as the concentration of phenyl phosphate, the amount of antibody attached to the electrode surface, the immersion time into a 2% BSA solution and the incubation time into IgG, protein A and AP conjugate solutions, were optimized. Electrochemical impedance spectroscopy was used to monitor all the steps involved in the preparation of the immunosensor. A linear calibration graph for IgG was obtained between 5 and 100 ng ml IgG, with a slope value of 11.8 nA ng ml, and a detection limit of 2.6 ng ml. These analytical characteristics are competitive with other IgG electrochemical immunosensor designs. The developed anti‐IgG (Tyr‐Aucoll‐graphite‐Teflon) immunosensor was applied to IgG determination in a spiked serum sample with a recovery of 103±6% for a 10 ng ml concentration level.