Highly loaded and dispersed Pt/C catalysts, used as cathodic electrocatalysts in low temperature fuel cells, were prepared using a new method involving the slow addition of a Pt precursor to a solution containing dispersed carbon powder and a reducing agent. During this process, the added Pt precursor was reduced instantaneously into fine particles and adsorbed onto the carbon surface in the solution. A Pt loading of 55 wt% was obtained, which was close to the nominal amount of Pt, 60 wt%, added in the preparation step. The average particle size of Pt was about 4.2 nm, according to X-ray diffraction. The surface area of the Pt measured by cyclic voltammetry was about 61.4 m2/(g of Pt). The activity of the prepared Pt/C, as an electrode of polymer electrolyte membrane fuel cell, was increased by 34.8% and 15.0%, according to the half- and single-cell tests, respectively, compared to the activity of one prepared using a conventional precipitation method.