In the light of the studies for the preparation of new devices for monitoring biochemical analytes the Chemically Modified Electrodes (CME) are a powerful tool for their versatile and reproducible behavior. In particular, the Self Assembled Monolayer (SAM) electrodes modified by thiols are very popular for the possibility of modulating the physico-chemical properties of thiol layer. Moreover, the metallic surface to which thiols can be attached plays a key role in the light of stability of the layer, accessibility of the electrode surface and possibility of fast electron transfer. In this work the electron transfer (ET) activity of cytochrome c (cyt c) adsorbed on thiol-based self assembled monolayer will be discussed in term of interactions between the protein and a redox couple probe, Fe(CN)(6)(3-)/Fe(CN)(6)(4-), added to the electrolytic solution. The outcomes point to a reaction mechanism similar to Saveant enzyme mechanism, with a rate constant value of 35,000 M-1 . s(-1), for the ET between cyt c and Fe(CN)(6)(3-/4-). The electrochemical characterization, by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), of mixed thiols layer in the presence of cyt c will be also discussed in term of thiol terminal functionalized groups and gold electrode substrate morphology. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.096204jes] All rights reserved.