Single phase γ’‐Fe4N type (Fe1−xNix)4N compounds (0≤x≤0.6) have been synthesized by heating iron‐nickel oxalates under a mixture stream of NH3 and H2. The compounds were investigated by x‐ray diffraction and Mössbauer spectroscopy. The results confirm that the lattice constants decrease with increasing content of nickel. Compared with the same compositional Fe1−xNix alloys, the average expansion of the unit cell (δV/V) is 16.7% for γ‐Fe‐Ni alloys. The Mössbauer study shows that the substitution of nickel atoms for iron atoms has a tendency to locate at the corner sites. When x=0.5, all of the corner sites are completely occupied by nickel atoms.