Scanning tunneling microscopy (STM) images of Pt ultrafine particles dispersed on silicon oxide and on aluminum oxide surfaces were obtained. The silicon oxide sample employed consists of a thin (ca. 0.6 nm thick) native silica film present on a Si(100) surface. The aluminum oxide sample was prepared by vacuum-depositing aluminum metal on a native-oxide-covered single crystal silicon surface, followed by its air oxidation. Model Pt/SiO2 and Pt/Al2O3 catalysts were prepared by vacuum-depositing Pt metal on those oxide surfaces. The STM observations of these sample surfaces were critically dependent on the tunneling conditions, and the optimum STM observation conditions for those supported metal catalyst systems were identified.