The　Ru/active　carbon　(AC)　ammonia　synthesis　catalyst　was　prepared　by　the　impregnation　method　using　coconut　as　the　support.　AC　was　impregnated　with　RuCl3　aqueous　solution.　The　samples　were　reduced　with　hydrogen,　hydrazine　hydrate　solution,　and　hydrazine　hydrate　vapors,　respectively.　The　three　Ru/AC　samples　were　impregnated　with　aqueous　solution　of　barium　nitrate　and　potassium　hydroxide.　The　Ru　content　was　6%　based　on　the　AC　mass　and　the　molar　ratio　of　Ru/K/Ba　was　1:3:0.3　in　these　catalysts.　The　catalyst　activity　correlated　with　their　surface　area　and　Ru　dispersion.　The　catalyst　that　was　reduced　with　hydrazine　hydrate　solution　at　pH　=　10∼13　in　the　range　from　room　temperature　to　90°　for　20　min　had　the　highest　surface　area　of　942　sq　m/g,　Ru　dispersion　of　17.72%,　and　catalytic　activity　of　20.36%　(volume　ratio　of　NH3)　at　low　pressure.　In　this　catalyst,　Ru　remained　in　the　metallic　state　when　the　sample　was　exposed　to　atmosphere.