A process is described for preparing cubic metallic nanoparticles, comprising: a) preparing an aqueous solution containing a source of a metal from group VIII, a reducing agent R1 and a stabilizer; b) preparing an aqueous solution containing a source of a group VIII metal and a stabilizer at a temperature strictly higher than 70° C. and less than or equal to 80° C.; c) mixing at least a portion of the aqueous solution obtained in step a) with the aqueous solution obtained in step b) to obtain, in the presence of a reducing agent R2, metallic nanoparticles in the cubic form representing at least 70% by number of the entire quantity of metallic nanoparticles which are formed; d) depositing said metallic nanoparticles derived from step c) on a support.