Fe3Mo3N was synthesized successfully via ammonolysis out of an oxidic precursor prepared by a modified Pechini route. Rietveld refinement using X‐ray powder data confirmed that the compound crystallizes in space group
with a lattice parameter of a=11.0777 Å. Group theoretical methods were applied to elucidate the relation between the crystal structure of Fe3Mo3N and that of the copper type. The high temperature behavior of Fe3Mo3N in ammonia gas was investigated by in situ powder X‐ray diffraction. In addition, the catalytic activity of our iron molybdenum nitride for ammonia decomposition was measured and compared to the activity of an industrial iron‐based catalyst. Both catalysts show similar performances.