Single phase gamma’-Fe4N type (Fe1-xNix)4N compounds (0 less than or equal to x less than or equal to 0.6) have been synthesized for the first time by controlled heat treatment of iron-nickel oxalates in a gaseous flow of NH3 rand H-2. The preparation processes were investigated using differential scanning calorimetry (DSC), X-ray diffraction and Mossbauer spectroscopy. The results confirmed that annealing of oxalates in the NH3 and H-2 atmosphere included the processes of dehydration, decomposition and reduction, nitrogenation and thermal decomposition of the nitrides. The decomposition and reduction occur simultaneously. The final products depend on the flow rate ratio of NH3:H-2 and the annealing temperature. The formation conditions for the single phase gamma’-Fe4N type (Fe1-xNix)(4)N compounds are related to the nickel concentration, with increasing nickel content, the nitrogenation temperature decreased, in contrast the flow rate ratio of NH3:H-2 increased.