The synthesis of aluminum nanoparticles (Amp) has raised promising perspectives these past few years for applications in energetic materials. However, because of their high reactivity, it is crucial to functionalize them before their use. In this work, we propose an original and simple chemical approach to graft spontaneously alkyl layers derived from alkyl halides at the surface of Alnp, by relying on the highly reductive character of these nanoparticles, when they are in the unoxidized form. Alnp were prepared in a glovebox and reacted with alkyl halides (RI and RBr) to give modified Alnp-R, as shown by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction, thermogravimetric analysis (TGA), and microscopy. The coating is made of alkyl multilayers, which were found to be strongly anchored at the Alnp surface, as it resisted 2 h of rinsing in toluene. An electrocatalytic electron transfer promoted by Alnp is proposed to describe the mechanism of this grafting reaction.