A recent experimental result shows that Pt L-edge XANES spectra for Pt small cluster are sensitive to CO adsorption. In the present study we try to extract useful information about geometric and electronic structures of these cluster by applying a full multiple-scattering approach for the XANES analyses. Detailed analyses provide us with information that some extent of change transfer plays an important role for the CO adsorption. We also discuss the plausible adsorption site on the Pt clusters.