The aim of this research is to study the effect of different preparation conditions for making carbon supported platinum catalysts by electroless deposition on the properties and performance of proton exchange membrane fuel cells (PEMFC). The studied parameters are platinum and formaldehyde concentrations, deposition time and the method of formaldehyde addition. By a univariate approach, the optimal preparation conditions of 20 wt% Pt/C catalyst are determined as using 10 g Pt l^(-1), two hours of deposition time and seven equally spaced additions of 0.15 M formaldehyde. SEM and TEM results indicate that the Pt/C catalyst attained has a small particle size (2-4 nm) and a good dispersion. The efficiency of the activation polarization of membrane electrode assembly (MEA) using these prepared catalysts is nearly that of commercial electrodes, but they have a significantly higher ohmic loss.