We have examined the adsorption of K on CeO@sub 2@ thin films and its effect on the adsorption of CO on Rh supported on the CeO@sub 2@. The K saturation coverage, i.e. the maximum coverage achievable before the onset of multilayer desorption, is ca. 1 x 10@super 15@ cm@super -2@. This is about twice what has been observed on Rh(111). It is similar to the CeO@sub 2@(111) surface density of 0.8 x 10@super 15@ cm@super -2@. The K exhibits three distinct desorption states near 450K, 600 K and 700 K. The K 2p core-level photoemission does not indicate a significant change in binding energy or the presence of multiple K states as a function of annealing temperature and coverage. CO dissociates when adsorbed on Rh on reduced CeO@sub X@. It is of interest to determine whether charge transfer from K to CeO@sub 2@ will also cause CO dissociation on Rh supported on K/CeO@sub 2@. CO desorbs from Rh on fully oxidized CeO@sub 2@ below 500 K and shows little evidence of O exchange with the ceria. The desorption is similar to CO on Rh(111). When K is present, the CO desorption occurs between 600 K and 700 K and shows considerable O exchange with the support. The high temperature desorption is similar to what was observed on K/Rh(111) which was ascribed to an interaction between the K and the CO. The high temperature desorption and O exchange are also similar to what has been observed for dissociated CO on Rh supported on reduced CeO@sub X@. For the system CO/Rh/K/CeO@sub 2@, there is no evidence of CO dissociation as indicated by the C 1s photoemission. The C 1s photoemission does indicate the formation of surface carbonates. Carbonates were not observed on either K/Rh(111) or Rh/CeO@sub X@. @FootnoteText@ @footnote 1@Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC.