A　series　of　Ce1-xZrxO2　(x　=　0,　0.2,　0.4,　0.5)　solid　solutions　were　prepared　by　the　micropore-diffused　coprecipitation　method　with　ammonia　solution　as　precipitation　agent.　Co0.2/Ce1-xZrxO2　catalysts　were　prepared　by　the　ultrasound-assisted　incipient-wetness　impregnation　method.　The　effect　of　the　Ce/Zr　molar　ratio　on　the　catalytic　activity　for　soot　combustion　was　investigated.　The　Co0.2/Ce1-xZrxO2　catalysts　gave　very　high　activity　for　soot　combustion　under　loose　contact　conditions　between　soot　and　catalyst,　and　the　catalytic　activity　of　Co0.2/Ce0.8Zr0.2O2　catalyst　was　the　highest　for　the　soot　combustion,　whose　T10,　T50,　T90,　and　SmCO2　were　316　°C,　385　°C,　413　°C,　and　99.9%,　respectively.　Compared　with　when　there　was　no　catalyst,　T10,　T50,　and　T90　decreased　by　136,　197,　and　226　°C,　respectively,　and　SmCO2　increased　by　45.9%.　This　catalytic　activity　for　soot　combustion　is　as　good　as　that　of　supported　Pt　catalysts,　which　was　the　best　catalyst　system　so　far　reported　for　soot　combustion　under　loose　contact　conditions.　All　the　samples　were　characterized　by　the　X-ray　diffraction,　transmission　electron　microscopy,　scanning　electron　microscopy,　Fourier　transform　infrared　spectroscopy,　and　UV-Vis　diffuse　reflectance　spectroscopy.　The　results　showed　that　nanometer　Ce1-xZrxO2　solid　solution　supports　can　be　prepared　by　the　micropore-diffused　coprecipitation　method.　The　average　particle　size　of　the　Ce1-xZrxO2　solid　solutions　was　about　10　nm.　Doping　Zr　affected　the　dispersion　of　Co　over　the　Ce1-xZrxO2　solid　solutions.　The　right　Ce/Zr　molar　ratio　was　beneficial　in　enhancing　the　catalytic　activity.　Temperature-programmed　reduction　with　hydrogen　measurements　showed　that　the　Co0.2/Ce0.8Zr0.2O2　catalyst　had　the　lowest　reduction　temperature　(203　and　298　°C),　which　was　in　good　agreement　with　its　best　catalytic　activity.　©　2010　Dalian　Institute　of　Chemical　Physics,　the　Chinese　Academy　of　Sciences.