In this paper, core-shell structured poly (indole-5-carboxylic acid) @ poly (3, 4-ethylenedioxythiophene) (PIn-5-COOH@PEDOT) composite was prepared by a facile two-step chemical oxidation method. The composite possesses large specific surface area, high stability, good electrical conductivity and redox activity, which was designed as label-free electrochemical immunosensing platform for the monitor of the prostate specific antigen (PSA). In this sensing system, PIn-5-COOH served as both signal molecule and antibody carrier. The coating PEDOT was used to enhance the conductivity and stability of PIn-5-COOH. Benefiting from the synergistic effects between PIn-5-COOH and PEDOT, the fabricated immunosensor exhibited a wide linear range of 0.01-25 ng mL(-1) and low detection limit of 3.4 pg mL(-1) (S/N = 3) for the assay of PSA, coupled with good selectivity, reproducibility and stability. The immunosensor is simple, sensitive, specific and reproducible, which could provide a potential approach for clinical diagnosis.