A series of the ruthenium catalysts was studied In ammonia synthesis. Magnesium oxide of the 94 m(2)/g BET surface, magnesium-aluminum (96 m(2)/g), boron nitride (190 m(2)/g) and high surface area, partly graphitized carbon (1188 m(2)/g) were used as supports for the active phase. All of the Ru catalysts (about 9% Ru) were promoted with barium. The NH3 synthesis tests were carried out at 400degreesC In a flow differential reactor supplied with an ammonia free or ammonia rich H2:N2=3:1 mixture at 63 bar and 90 bar. Large differences among the catalysts were found. The Ba-Ru/C system proved to be most active. The reaction rate over Ba-Ru/C was more than two orders of magnitude higher than that over the fused iron catalyst, both rates being reffered to the metal mass.