The chemically modified electrode (CME), which was constructed by adsorbing the mediator methylene green (MG) onto the spectrographic graphite electrode, shows significant electrocatalytic activity to the oxidation of reduced nicotinamide adeninedinucleotide (NADH), reducing oxidation overpotential by 500mV. In the potential range from -0.25 V to +0.1V the adsorbed mediator MG behaves as one-electron reversible redox process involving one proton. In the medium of 0.1mol/dm(3) phosphate buffer (pH=7.0) the surface formal potential E degrees ' and apparent electron-transfer rate of the adsorbed mediator MG were found to be -0.14V and 4.4s(-1), respectively. The CME was tested as a electrochemical NADH detector, which shows high sensitivity and good stability. The CME was also characterized by ESCA and ATR.