The encapsulation (decoration) of Rh nanoparticles supported on a TiO2(110) surface was studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). In the case of a stoichiometric and well-ordered TiO2(110)-(1 x 1) surface covered by 3 monolayers (ML) of rhodium, there is no indication for thermally induced decoration of the metal particles by the suboxide phase of titania in the temperature range 300-800 K in ultrahigh vacuum (UHV). The encapsulation can be induced, however, by a few minutes annealing in a H-2 atmosphere of 10(-4) mbar at 750 K. The islands of TiOx phase on the top of the rhodium particles were clearly detected by STM. In the case of specially grown giant Rh crystallites (diameter of 10-15 nm) annealing in H-2 at 750 K results ill dramatic morphological changes (corrosion or disruption) of the original nanoparticles accompanying the encapsulation process. Pretreatment of the stoichiometric TiO2(110)-(1 x 1) surface by Ar+ bombardment (creation of surface and subsurface Ti3+ states) and the postdeposition of Rh on it results in encapsulation of Rh particles after annealing in UHV (in the absence of hydrogen).