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The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance. Herein, Pt/CeO2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method, and their catalytic performance in CO oxidation was investigated. XRD, TEM, XPS and H2-TPR were used to identify the states of Pt particles on the support surface, as well as their effect on the performance of the catalysts. Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity. Under the oxidative treatment at low temperature, the Pt-O-Ce interaction plays an important role in improving the catalytic activity. After calcining at high temperature, enhanced Pt-O-Ce interaction results in the absence of metallic Pt0 on the support surface, as evidenced by the appearance of Pt2+species. It is consistent with the XPS data of Pt/CeO2, and is the main reason behind the deactivation of the catalyst. By contrast, either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt0 state on the SiC surface even after aging at 800 ℃ in an oxidizing atmosphere. Thus, the Pt/SiC shows better thermal stability than Pt/CeO2. The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature, but strong interactions may induce serious deactivation of catalytic activity.