The Chini-type Pt carbonyl clusters ([Pt-3(CO)(6)](n)(2-), n = 4, 5, 6) and other GO-stabilized Pt clusters were synthesized by gamma-radiolysis, and their structures, when supported on carbon and alpha-alumina, were investigated by X-ray absorption spectroscopy (XAS). It was found that the stacking prismatic structure of triangular units in Chini clusters was transformed, when supported on carbon, into another structure in which the trimeric units are conserved but are now arranged in a planar monolayer, Some carbonyl groups remain to be ligated to Pt atoms under nitrogen atmosphere. However, on contact with the air, the carbonyl clusters are partially transformed into fee Pt clusters. When supported on alpha-alumina, a more important structural evolution of supported clusters with a size growth is observed, Two groups of platinum clusters are obtained: the first one with a Pt-Pt distance corresponding to the intratriangular distance present in the Chini clusters, and the second one constituted of larger fee clusters with a Pt-Pt distance close to the bulk one.