Cesium-promoted cobalt molybdenum bimetallic nitride Co3Mo3N catalyst was found to give higher productivity of ammonia than a doubly promoted iron catalyst. Molybdenum nitride catalysts were prepared by nitridation of the corresponding oxide precursors with ammonia gas via a temperature-programmed reaction up to 973 K. The precursors were molybdenum trioxide or molybdenum bimetallic oxide prepared via a mixed solution of ammonium molybdate and metal (Co, Ni, and Fe) nitrate. Ammonia synthesis was carried out with a 0.4 g of catalyst at 673 K under 0.1 MPa with a flow rate of 60 ml min(-1) of N-2 +/-3H(2), The simple Mo2N was less active (35 mu mol h(-1) g-cat(-1)) and deactivated soon. Co3Mo3N prepared from cobalt molybdate hydrate was active (179 mu mol h(-1) g-cat(-1)) and stable. The activity of Co3Mo3N was increased (652 mu mol h(-1) g-cat(-1)) after being treated with the reactant gas at 873 K for 6 h after the passivation with 1% of O-2 at 298 K. The corresponding molybdenum bimetallic nitrides with nickel or iron were also prepared; however, they were not as active as Co3Mo3N. The activity of Co3Mo3N was increased by the addition of alkali promoter. Cesium was a more effective promoter than potassium, suggesting an electronic effect. 2 mol% Cs addition was found to give the maximum activity after the reactant gas treatment at 873 K for 6 h (986 mu mol h(-1) g-cat(-1)).