Slight enhancement of saturation magnetization to 219Am2kg−1 was observed from 199Am2kg−1 for the original α-Fe on the intermediate nitrided mixture of “α′′-Fe16N2” with residual α-Fe among the low temperature ammonia nitridation products under 5T magnetic field at room temperature. The value changed not linearly against the yield as had been expected. Crystal structure refinement indicated that the phase similar to α′′-Fe16N2 had deviations on its lattice constants and positional parameters, compared to previously reported values for α′′-Fe16N2. Spin-polarized total energy calculations were performed using the projector-augmented wave method as implemented in the Vienna ab-initio simulation package (VASP) to calculate magnetic moment on the refined crystal structure of the intermediate “α′′-Fe16N2”. The calculations supported the observed magnetization enhancement in the intermediate nitridation product. Crystal structural parameters slightly change in the intermediate nitrided “α′′-Fe16N2” from those in α′′-Fe16N2 to show the magnetization maxima in the mixture of “α′′-Fe16N2” and the residual α-F. Display omitted ► Larger magnetization was observed than the value of Fe16N2 on its intermediate nitrided mixture with residual α-Fe. ► The enhancement was related to the crystal structural deviation from Fe16N2 on the intermediate nitride. ► It was supported by spin-polarized total energy calculation using the deviated structure.