This work reports on the design of novel aryl-modified gold nanoparticles using diazonium chemistry. The organically capped gold nanoparticles served as electrocatalysts of the ethanol oxidation. First, The Turkevich method was used to synthesize 20 nm-sized gold nanoparticles that were readily arylated using diazonium salts. Then, individually, the diazonium salts AB and DMB were synthesized and served for the arylation of gold nanoparticles. TEM, XPS and TGA/DTA confirmed the formation of an aryl layer attached to nanoparticles with different thickness depending on the initial concentration of diazonium salts. Subsequently, the catalytic properties of the AuNPs were investigated for ethanol oxidation before and after grafting of diazonium salts. In this regard, by modifying gold nanoparticles with diazonium salts, the following results were obtained: 1-Maintaining the catalytic property of nanoparticles for ethanol oxidation after grafting the organic layer. 2-In comparing the catalytic properties of nanoparticles modified by a diazonium AB salt or two types of AB and DMB salts, it was found that NPs/AB at optimal concentration of diazonium salt (510 -5 M) there was no significant current intensity loss; however it was observed, this current intensity drop was greater in the use of two types of salt. This could be due to the decrease in the active surface of gold nanoparticles through further aggregation of these grafted nanoparticles because of the hydrophobicity of DMB salts. 3-Using the co-grafting of salts AB and DMB and determining the appropriate ratio and salts concentration, it was shown that surface engineering permitted to control the number of layers and also the ability to use other diazonium salts. 4-It is also noteworthy that using two diazonium salts AB and DMB in the same concentration (510 -5 M) led to a more homogeneous organic layer on the nanoparticles than using a single AB diazonium salt. This gives us better control over the homogeneity and thickness of the organic layer to keep working. 5-However, highest ethanol oxidation peak intensity was obtained for the lowest concentration of single AB diazonium concentration. Further dilution of AB by mixing with DMB resulted in les efficiency, likely due to barrier effect of the hydrophobic DMB methyl groups which hamper access of ethanol molecules to the nanocatalyst.