Rhodium in nanosize (1-3 nm) was prepared by vapor deposition of Rh on a well-ordered TiO2(110)1 x 2 single crystal. The morphology and the sizes of Rh had been determined by scanning tunneling microscopy in ultrahigh vacuum. The adsorption of CO at 300 K induces the disruption of Rh crystallites as indicated by a drastic decrease in the size of Rh particles. At higher temperature it leads to the re-forming of the Rh cluster.