Co-Mo catalysts contg. Cs (0.25-3.0% by mass) were obtained by redn. of precursors with NH3 at 700 degrees C. The precursors were derived from aq. solns. of (NH4)(6)Mo7O24, Co(NO3)(2) and CsOH. The anal. of catalysts by X-ray diffraction and anal. of the diffraction profiles by Rietveld method showed the presence of Co2Mo3N and Co3Mo3N phases depending on the content of Cs in the catalyst. Activities of the catalysts were tested under lab. conditions of the synthesis of NH3 at 400 degrees C and 10 MPa. The reaction rate const. was detd. by measuring the flow of the reaction gases and NH3 concns. The highest activity was achieved for the catalyst contg. Cs 1.7% by mass. The catalysts used for the activity detns. were then subjected to aging (650 degrees C, 18 h) and their activity was repeatedly detd. Thermal treatment resulted in sintering of crystallite Co3Mo3N phase and decreasing the activity of catalysts.