Experimental HREM combined with computer simulation, digital image processing, and SAED techniques have been fruitfully applied to the nanostructural characterization of a Pt/CeO2 catalyst reduced at temperatures ranging from 473 to 1223 K. Metal decoration effects were detected upon reduction at 973 K. Alloying phenomena could be observed only at the highest reduction temperatures, The crystallographic analysis of the HREM images shows that CePt5 is the only intermetallic phase present in the catalyst. Likewise, preferential orientation relationships were observed in the growth of the alloy microcrystals on ceria.