Monodisperse platinum nanoparticles with controlled size were synthesized by polyol synthesis and supported on γ-Al₂O₃, SiO₂ and carbon nanotubes (CNT) by the colloid deposition method. The average size of Pt nanoparticles in colloidal solutions and on supports were determined by TEM images and from XRD patterns. The size of Pt nanoparticles supported on SiO₂ and CNT determined from XRD patterns is in a good agreement with size obtained from the TEM analyses. There were shown that no agglomeration and size changing of Pt nanoparticles on these supports were observed. All these findings illustrate that the method of colloid deposition allows one to obtain catalyst with monodisperse platinum nanoparticles of controlled size deposited on different supports without changing the nanoparticle’s size and morphology.