Copper　supported　on　ceria　and　ceria-magnesia　catalysts　were　synthesized　and　used　for　NO　reduction　by　CO.　The　supports　and　the　subsequent　Cu　catalysts　were　prepared　by　citric　acid　sol-gel　and　impregnation　methods,　respectively.　Based　on　XRD,　TPR　and　EPR　measurements,　it　is　found　that　the　Mg　addition　promotes　not　only　the　dispersion　of　CuO,　but　also　the　doping　of　copper　ions　into　CeO2　matrix.　A　redox　treatment　favors　some　of　copper　ions　in　the　octahedral　sites　of　CeO2　substituting　the　lattice　sites　of　Ce4+.　Combining　the　results　of　activity　test,　we　found　that　the　formation　of　copper-substituted　Cu-O-Ce　solid　solution　promotes　the　catalytic　activity　of　the　catalysts.　Also,　the　ways　that　MgO　acts　on　the　dispersion　of　CuO　and　the　formation　of　Cu-O-Ce　solid　solutions　were　investigated　with　the　aid　of　TEM,　TGA　and　XRD　techniques.　The　results　of　these　studies　suggest　that　magnesia　crystallites　undergo　a　phase　evolvement　during　the　preparation　process　of　Cu/MgO-CeO2,　leading　to　the　reconstitution　of　the　support　and　hence　the　improvement　of　copper　dispersion,　BET　surface　area,　pore　volume,　as　well　as　the　doping　of　copper　ions　into　the　CeO2　matrix.　©　2009　Elsevier　B.V.　All　rights　reserved.