The simple and efficient method for preparing sensitive carbon nanotube/polysulfone/RIgG immunocomposite is described. The membrane of the modified disposable screen-printed electrochemical immunosensor is based on phase inversion method. Carbon nanotube/polysulfone membrane acts both as reservoir of immunological material and transducer while offering high surface area, high toughness and mechanical flexibility. The comparison with graphite/polysulfone/RIgG immunosensors shows a much higher sensitivity for those prepared with carbon nanotubes coupled with polysulfone (PSf). The membrane was characterized by scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), laser profilometer and by atomic force microscopy (AFM). The purity of the materials was evaluated by thermogravimetric analysis (TGA). The roughness value is doubled when MWCNTs are used instead of graphite into the PSf membranes and the incorporation of antibodies enhances the dispersion of the carbon with the polymeric membrane reducing the roughness in all cases. This biosensor was based on the competitive assay between free and labelled anti-RIgG for the available binding sites of immobilized rabbit IgG (RIgG). The RIgG was incorporated into the polysulfone membrane by a phase inversion method. Horse radish peroxidase (HRP) enzyme was used as label and hydroquinone as mediator. The detection limit for competitive assay was determined to be 1.66 microg/ml. the linear range of anti-RIgG from 2 to 5 microg/ml and the C(50) was found at 3.56 microg/ml. The sensitivity is five times higher for MWCNT than for graphite electrodes, showing lower unspecific adsorption.