In this study, an electrochemical immunosensor was developed using gold nanoparticles (AuNPs), 3,4-ethylenedioxythiophene (EDOT), and pyrrole (Py) to detect carcinoembryonic antigen (CEA) sensitively. Firstly, the electrocopolymerization of PPy and EDOT was carried out on a pencil graphite electrode (PGE) by the chronoamperometry method (p(Py-co-EDOT)/PGE). Then, gold nanoparticles were electrochemically deposited on the prepared p(Py-co-EDOT)/PGEs by the chronoamperometry method. The characterizations of the developed label-free immunosensor (AuNPs/p(Py-co-EDOT)/PGE) were carried out using CV, EIS, XPS, SEM, EDX, and FTIR methods. Antibody concentration, antibody immobilization time, and immunocomplex time were optimized using differential pulse voltammetry (DPV). After optimal conditions are determined, the DPV peak current of the immunosensor decreases linearly with increasing CEA concentration of 0.001-100 ng mL(-1). The detection limit was calculated as 0.741 pg mL(-1) from the calibration graph (S/N=3). The developed sensor showed excellent anti-interference ability against ascorbic acid, bovine serum albumin, dopamine, and glucose. The applicability of the developed sensor to real samples was investigated, and good recovery values were obtained. As a result, the AuNPs/p(Py-EDOT)/PGE provides low-cost, selective, and rapid detection of CEA. Our findings suggest the present immunosensor is a good candidate for application in clinical screening.