Effects of different gases (CO, NO, H-2, CO2) on the morphological changes of Rh nanoparticles deposited on TiO2(110)-(1 x 2) surface were studied by scanning tunneling microscopy. The planar model catalyst surface was prepared by evaporation of Rh on TiO2 at room temperature followed by annealing in UHV. By the variation of the Rh content and the annealing temperature Rh nanoparticles can be produced in the range of 1-10 nn. A very rapid disintegration of the supported Rh nanoparticles of 1-2 nn to atomically dispersed Rh was observed at 300 K even after a few minutes exposure to a pressure of 10(-1) mbar CO. For particle sizes of 3-4 nm the CO-induced process became slower, and for larger Rh clusters (8-10 nm) it did not occur at all even at higher CO pressure. Keeping the atomically dispersed Rh in CO above 500 K led to the reformation of the Rh clusters but of larger size. The CO-induced agglomeration was also observed for larger Rh particles (5-6 nm) above 500 K. The adsorption of NO on Rh nanoparticles also resulted in the disruption of Rh-x crystallites at 300 K. It was not observed, however, in the presence of H-2 and CO2, which was explained by the different nature of their interaction with Rh.