In this research, a comprehensive investigation of nanoparticle formation during electrodeposition of Pt, Pd, and Pt-Pd from 1 mM PdCl2 and 1 mM H2PtCl6 in the presence of 0.5 M H2SO4 electrolyte on glassy carbon electrode was conducted. By employing cyclic voltammetry and chronoamperometry together with the scanning electron microscopy and X-ray photoelectron spectroscopy, some kinetic parameters were obtained and the mechanisms of Pd and Pt nucleation, microstructure, and physical properties were clarified. It was shown that during Pt-Pd particles formation, the electrodeposition of Pd was controlled by diffusion of Pd2+ ions, whereas Pt electrodeposition was a charge transfer-controlled process. In addition, as a result of the higher rate of Pd nucleation, at the initial times of co-electrodeposition, Pd clusters were formed, then the Pt was electrodeposited over the pre-nucleated/pre-grown Pd. Consequently, it leads to Pt enrichment on the nanoparticle surface (84%). In other words, the co-electrodeposition of Pt-Pd not only reduces the size of deposited particles but also can minimize the overpotential required for deposition. Furthermore, as XPS results supports, the synthesized nanoparticles have alloyed/partially alloyed structure rather than core-shell or separate single elemental nanoparticles. [GRAPHICS] .