An electrochemical immunosensor was developed to determine carcinoembryonic antigen (CEA). A sensor platform was created using a three-dimensional (3D) porous chitosan cryogel incorporating poly(3,4-ethylenedioxythiophene), Prussian blue, and gold nanoparticles modified screen-printed carbon electrode (CS-AuNPs-PEDOT-PB cry/SPCE). The platform was activated with anti-CEA and measurement of CEA was based on the formation of an immunocomplex proportional to CEA concentration in the sample. CEA was detected using differential pulse voltammetry, which measured the change in reduction peak current of PB in response to the immunocomplex formed. Crucially, PEDOT stabilized PB and amplified the redox current of PB. Under optimal conditions, the proposed immunosensor displayed a high sensitivity, a linear range from 1.0 × 10⁻⁴ to 1.0 × 10³ pg mL⁻¹, and a detection limit of 5.05 × 10⁻⁵ pg mL⁻¹ in 0.10 mol L⁻¹ phosphate buffer containing 0.10 mol L⁻¹ KCl (PBS) (pH 7.00). Reproducibility was excellent (RSD of less than 5.3 %, n = 6), and reusability (sensitivity > 90 % for 36 individual CEA measurements), stability (90 % sensitivity at 5 weeks), and selectivity were good. Additionally, this electrochemical immunosensor successfully quantified CEA in real samples, achieving good recoveries and results agreed (P > 0.05) with the immunoturbidimetry technique.