A simple method is described by which supported Ir nanoparticles can be fabricated in desired uniform sizes in the range of 1.5-20.0 nm with constant interparticle distances. The nanoparticles are characterized by STM. The method exploits the significant differences in the diffusion rates of metal adatoms and nanocrystallites, and consists of two steps: (i) vapor deposition of Ir metal in predetermined concentrations on titania at 300 K with a postannealing at 1200 K, and (ii) subsequent evaporation of Ir on this surface at 1200 K.