Nanostructured electrodes can be used as model catalysts in order to gain a basic understanding of electrocatalytic properties. In particular, the influence of particle size and particle dispersion of noble metal catalysts and a possible influence of the support material can be studied in detail. Electrocatalytic reactions such as the hydrogen oxidation reaction (HOR), the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) are important for technical applications. Hence, palladium and platinum as typical catalysts were investigated on Au(111) substrates regarding the HOR, HER and ORR. A significant increase in catalytic activity was found for Pd and Pt deposited on Au(111) where, with a decreasing amount of deposited metal, an increase of specific activity is observed which is contrary to expectations. A different behaviour was found for the ORR, where, according to expectations, the reactivity increases with increasing amounts of Pt. Parameters influencing the electrocatalytic activity of nanostructured surfaces, such as strain of the overlayers induced by the support and a possible direct involvement of the Au(111) surface in the mechanism of HER, are discussed.