Platinum nanoparticles have been prepared by potentiostatic multipulse electrodeposition with controlled nucleation and growth on freshly cleaved and electrochemically oxidized highly oriented pyrolytic graphite. The influence of the applied potential sequence on the size distribution was investigated. For short electrolysis times, the deposition of nanoparticles takes place via a progressive nucleation mechanism. A narrow size distribution was obtained by controlling independently the nucleation and growth steps, and particles with heights between 52 and 1.4 nm could be prepared by altering the pulse parameters. Anodic oxidation of the substrate had a large influence on the particle size, resulting in the preparation of particles 1.4 nm in height. XPS demonstrated that Pt particles of small size were readily oxidized. The rate of electrochemical methanol oxidation showed a dependence on the particle size, and no oxidation of methanol could be observed for the smaller sizes investigated.