A biosensor for the determination of alcohol based on cysteine (Cys) nanolayers has been constructed. The utilization of the redox-inactive, self-assembled monolayer (SAM) modified gold ultra micro-electrode (UME) for NADH electroanalysis is introduced as a new modified gold Cys-UME. This Cys-UME prevents fouling and was found to be stable and ill-defined under subsequent potential sweeps, and different NADH concentrations. NADH oxidation gave a linear correlation between the peak current and NADH concentration (1-5 mM). Also, excellent electro-catalytic activity (enhancing the oxidation peak current) was observed towards NADH oxidation, with activation overpotential of about 250 mV lower than that of the bare electrode. The use of different alcohol concentrations in the presence of alcohol dehydrogenase (ADH) gave an increase in the NADH oxidation peak current, indicating that the electrochemical NADH oxidation at mild potentials could lead to an enzymatically active NAD ?.