Cobalt molybdenum nitrides can be obtained from the oxidic precursor by reaction with gaseous ammonia. Despite the large number of works regarding catalytical properties of these compounds, there are relatively few reports about the initial transformation from oxide to nitride. In this work, the influence of the precursor structure on the active phase formation and catalytic properties of cobalt molybdenum nitrides is examined. Oxidic precursors were obtained by precipitation at different pH values controlled by the addition of aqueous ammonia. The parameters of the precipitation process affected the composition and properties of the materials. The ammonolysis of NH4Co2OH(MoO4)2·H2O was investigated in situ with the use of X-ray powder diffraction and thermogravimetry. The ammonia synthesis activity of the obtained catalysts was compared to the reference iron catalyst. The formation of the Co3Mo intermetallic phase was suggested as the factor governing high activity.