The selective metallization of a semiconducting oxide (ceria) supported on an insulating oxide (silica) is investigated through new methods involving optical and electronic properties of the components of the composite. Supported ceria particles in the nanometer range are studied. Two methods of Pd deposition are applied : (i) electroless deposition via laser activation of the composite suspension in the Pd precursor solution; (ii) UV photoreduction of Pd on the composite. Electroless deposition results in a wide distribution of metal particle size, from 2-3 nm to 600 nm, while some ceria particles are not metallized at all. On the contrary, photoreduction fixes the Pd on ceria selectively, yielding Pd particles with sizes comparable to that of the ceria. The influence of various parameters governing the metal deposition is discussed.