Cyclic voltammetry (CV), transmission electron microscopy (TEM) and C-13 nuclear magnetic resonance spectroscopy (NMR) were employed to investigate the particle size and surface morphology of fuel cell grade platinum black samples as received and prepared under three different cleaning methods. The Pt particle growth was most markedly caused by extensive CV treatment moderately by cleaning with chromic acid, and negligibly by holding the potential at 250 mV. Even single anodic sweep CV removed Pt adatoms; in contrast, cleaning with chromic acid and holding the potential at 250 mV did not. Our results demonstrate that a cleaning method should be chosen with the knowledge of its effect on the metal surface and particle size. The possibility of detecting the particle size change due to cleaning procedures by C-13 NMR is also discussed.