Ru/CeO2　catalysts　were　prepared　by　the　co-precipitation　method　using　six　precipitants,　K2CO3,　NH3　center　dot　H2O,　(NH4)(2)CO3,　KOH,　NH4HCO3　and　KHCO3,　used　for　the　ammonia　synthesis　and　characterized　by　N-2　adsorption-desorption,　X-ray　fluorescence　spectroscopy,　X-ray　diffraction　and　H-2　temperature-programmed　reduction　to　explore　the　cause　resulting　in　their　significant　difference　of　catalytic　activity.　The　ammonia　synthesis　activity　of　Ru/CeO2　catalyst　prepared　using　NH4HCO3　as　the　precipitant　was　14.46%　at　10　MPa,　10000　h(-1),　450　degrees　C,　which　was　higher　than　those　obtained　by　other　precipitants.　The　samples　prepared　using　the　rest　four　precipitants　presented　lower　activity　for　ammonia　synthesis.　The　type　of　precipitant　not　only　significantly　affects　the　coprecipitation　of　ruthenium　and　cerium　ions,　but　also　affects　the　reduction　of　the　surface　oxygen.　The　high　catalytic　activity　of　Ru/CeO2　catalyst　prepared　using　NH4HCO3　can　be　attributed　to　the　synergism　among　the　increase　in　ruthenium　loading,　the　higher　dispersion　of　ruthenium　particles,　and　the　easier　reduction　of　surface　oxygen　of　the　support.