Monodispersed Pt-1, Pt-2, and Pt-3 clusters have been deposited on an atomically clean SiO2 film in ultrahigh vacuum to surface coverages of about 0.01 monolayer. CO chemisorption/desorption experiments at 300 K exhibit a distinct 340 K CO desorption state with an activation energy of similar to 16 kcal/mol. Comparisons with CO desorption from Pt(111), Pt(112), and bulk Pt films on SiO2 are made, showing that the 340 K CO desorption process is a unique feature of highly dispersed Pt atoms on SiO2. CO desorption from other Pt sites is also detected exhibiting higher desorption activation energies, but the nature of these sites cannot be ascertained in these experiments with certainty.