The deposition of platinum in Nafion (NF) and polyvinylpyridine (PVP) films (d = 1 mu m) was carried out from 5 mM Na2PtCl4 + 0.5 M H2SO4 and 5 mM Na2PtCl4 + 0.05 M H2SO4 + 0.5 M Na2SO4 solutions potentiostatically (at 0.1 V vs RHE). The possibility is shown of preparing ultradispersed deposits with a particle diameter of similar to 3 nm. The rate of hydrogen evolution on Pt deposits in NF and PVP films in the range of small overvoltage (eta < 30 mV) is limited by the removal of hydrogen from the external surface of the electrode. For Pt/NF/GC electrodes this process occurs at smaller overvoltage values than that on a smooth Pt surface. The higher hydrophobicity of the Pt/NF surface probably facilitates the formation of bubbles and reduces hydrogen supersaturation in the near-electrode layer. The electrocatalytic behavior of platinum deposits in NF and PVP was studied in the reaction of methanol and formic acid oxidation. The role of the dimensional effect and metal particles interaction with the polymeric matrix in electrocatalytic processes was demonstrated. In the Pt/PVP/GC system, the first effect is more pronounced, and in the Pt/NF/GC system the second effect is predominant.