This work aims at investigating and comparing the electrocatalytic properties of gold nanoparticles before and after grafting aryl groups from one or two types of diazonium salts in the oxidation of ethanol. In addition, the initial diazonium salt concentrations were step wisely monitored in order to tune the composition and grafting density of the surface bound organic layer while maintaining the catalytic properties of gold nanoparticles as well as their stability, therefore preventing their aggregation (maintaining a higher level of active nanoparticles). Gold NPs of controlled size in aqueous solution were prepared and stabilized with citrate salts via the Turkevich-Frens method . We have functionalized NPs through the reductive grafting reaction of diazonium salts, focusing on the tuned attachment of carboxyphenyl groups. The main challenge of this work was to control the number of acid functions introduced, without compromising the catalytic properties of gold NPs via excessive arylation. To address this issue, mixtures of para-carboxybenzenediazonium and 3,5dimethylbenzenediazonium salts were used. The former serves as a basis for coupling with other functional groups for hybrid materials with a variety of applications, while the latter is used to hamper any possible oligomerization and growth of thick aryl that passivates the surface of the nanocatalyst . Different concentrations of diazonium salts AB and DMB were investigated to obtain optimal conditions for ethanol oxidation. Catalytic activity of the pristine and diazonium-modified NPs vis-à-vis ethanol oxidation reaction was assessed by cyclic voltammetry.