Modified　zirconia　(ZrO2)　were　synthesized　by　high　temperature　calcination　of　ZrO(OH)2　gels　digested　in　alkalic　solution;　with　the　modified　ZrO2　as　support,　ruthenium　catalysts　for　ammonia　synthesis　were　prepared　with　K2RuO4　solution.　The　catalysts　were　characterized　by　X-ray　diffraction　(XRD),　temperature　programmed　reduction　of　hydrogen　(H2-TPR),　temperature　programmed　desorption　of　CO2　(CO2-TPD),　nitrogen　sorption,　X-ray　fluorescence　spectroscopy　(XRF),　and　CO　chemisorption;　the　relationship　between　the　catalyst　structure　and　its　catalytic　activity　was　especially　discussed.　The　results　revealed　that　the　digestion　either　in　KOH　or　NH4OH　solution　can　enhance　the　surface　area　of　the　ZrO2　support,　while　digestion　in　KOH　is　able　to　obtain　the　support　with　high　basicity,　which　benefits　to　getting　the　ruthenium　catalyst　of　high　activity.　The　strong　basicity　of　the　modified　ZrO2　support,　rather　than　the　high　ruthenium　dispersion,　plays　a　more　important　role　in　enhancing　the　activity　of　the　supported　ruthenium　catalyst.　For　ammonia　synthesis　under　425　°C,　5　MPa　and　a　space　velocity　of　10　000　h-1,　NH3　outlet　concentration　over　Ru/ZrO2-KOH　is　5.96%,　which　is　11%,　143%　and　103%　higher　than　those　of　K-Ru/ZrO2-NH4OH,　K-Ru/ZrO2-CP　and　Ru/ZrO2-NH4OH,　respectively.