A label-free impedimetric immunosensor based on a conjugated poly(pyrroleN-hydroxy succinimide) (PPyr-NHS) polymer covered disposable indium tin oxide electrode (ITO) was fabricated for the ultrasensitive determination of interleukin 6 (IL 6) antigen. In this sensing platform, the PPyr-NHS polymer, which carried a number of succinimide groups on its end side, was used as a matrix material for the first time. This synthesized polymer had excellent biocompatibility and good electrical conductivity. In addition, the utilization of this material as a matrix material provided direct immobilization of the IL 6 receptor (IL6R), which was employed as a biorecognition element. The preparation of the working electrode, the successful attachment of IL 6R and specific interaction between IL6R and IL 6 antigen were confirmed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Moreover, the working electrode surface was characterized by Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy during its construction. An impedimetric method was employed for the quantification of IL 6 antigen. Under optimized experimental conditions, the designed sensing platform could detect IL 6 antigen with a wide detection range from 0.03 pg mL(-1)to 22.5 pg mL(-1)with a relatively low detection limit of 10.2 fg mL(-1). In addition, the developed biosensor had outstanding sensitivity and specificity, good repeatability and reproducibility, high stability and reusability. Additionally, the designed sensing tool was successfully used in human serum samples. Consequently, the suggested immunosensor was clinically useful in the early detection of prostate cancer by direct determination of the serum IL 6 antigen level after simple dilution.