The electro-oxidation of dihydronicotinamide adenine dinucleotide (NADH) on three low-index basal single crystal gold faces was studied in a phosphate buffer solution. The reaction was found highly structure-sensitive; the Au(100) and Au(111) faces showed a high electrocatalytic activity, while the Au(110) face was much less active. The high electrocatalytic effect was attributed to the oxidation-mediator ability of the partially discharged OH(1-r)- species on the gold surface. The structural effect of the gold faces on the electro-oxidation of NADH may result from the difference in the adsorption of NAD+, via its pyridine moiety as the adsorption site, on the different gold faces. The possibility of developing a highly sensitive NADH sensor based on the electrochemical faceting technique is suggested.