In this study, an impedimetric immunosensor based on polymer poly(thiophene)-graft-poly(methacrylamide) polymer (P(Thi-g-MAm)) modified indium tin oxide (ITO) electrode is developed for the detection of the Neuron Specific Enolase (NSE) cancer biomarker. First, the P(Thi-g-MAm) polymer is synthesized and coated on the ITO electrode by using a spin-coating technique. P(Thi-g-MAm) polymer acts as an immobilization platform for immobilization of NSE-specific monoclonal antibodies. Anti-NSE antibodies are utilized as biosensing molecules and they bind to the amino groups of P(Thi-g-Mam) polymer via glutaraldehyde cross-linking. Spin-coating technique is employed for bioelectrode fabrication and this technique provides a thin and uniform film on the ITO electrode surface. This bioelectrode fabrication technique is simple and it generates a suitable platform for large-scale loadings of anti-NSE antibodies. This immunosensor exhibits a wide linear detection range from 0.02 to 4 pg mL(-1) and with an ultralow detection limit of 6.1 fg mL(-1). It reveals a good long-term stability (after 8 weeks, 78% of its initial activity), an excellent reproducibility (1.29% of relative standard deviation (RSD)), a good repeatability (5.55% of RSD), and a high selectivity. In addition, the developed immunosensor is proposed as a robust diagnostic tool for the clinical detection of NSE and other cancer biomarkers.