In this work, a two-step method was developed for the fabrication of a graphene sensing platform doped with poly(3,4-ethylenedioxythiophene)/Au nanoparticles (AuNPs/PEDOT/GR). PEDOT nanorods grown on graphene oxide nanosheets (PEDOT/GO) were firstly synthesized by liquid-liquid interfacial polymerization, followed by the chemical reduction of HAuCl4 by NaBH4. During the reduction process, GO doped in the PEDOT was also reduced to a more conductive form of GR. The obtained AuNPs/PEDOT/GR showed excellent conductivity and large surface area. Thus, a simple and sensitive label-free immunosensor based on AuNPs/PEDOT/GR nanocomposite has been proposed to detect carcinoembryonic antigen (CEA) by measuring the change of electrochemical response before and after the immunoreaction. Under the optimized conditions, the linear range of the proposed immunosensor is estimated to be from 0.0004 to 40 ng mL-1 (R2 = 0.9969) and the detection limit is estimated to be 0.1 pg mL-1 at a signal-to-noise ratio of 3. Moreover, the immunosensor was examined for use in the determination of CEA in real human serum samples with satisfactory results.