An electrodeposition process of platinum and platinum-based alloy nano-particles with addition of ethylene glycol is disclosed. An acidic solution which contains metal chloride includes at least one platinum-based chloride and the alloy thereof, and ethylene glycol are introduced into a reactor as an electrodeposition solution. By applying an external negative potential, platinum particles or platinum-based alloy particles are deposited on the substrate. The above acidic solution is able to provide ionic conductivity during electrodeposition. The added ethylene glycol effectively enhances the removal of chlorine from metal chlorides. Meanwhile, ethylene glycol is used as stabilizer to prevent the particles from aggregation onto the substrate, thereby increasing the dispersion of deposited particles.