This article aims to investigate the effect of soluble and insoluble nitrogen on mechanical properties of stainless steels. Reference steel contains about 14.42%Ni and 0.012%N. Two developed steels have the same base chemical composition of the reference steel except Ni and N contents. One of the developed steels has 6.54%Ni and 0.232%N and the other has 0.452%N and nearly nickel free (0.089%Ni). The produced steels were forged, heat-treated, and tempered. The microstructure of steels was mainly austenite, and grain size decreases as nitrogen content – especially nitrides-increases. Yield and ultimate tensile strength of reference steel are less than that of steels containing nitrogen. Strengthening mechanisms contribution to the strength of both soluble and insoluble nitrogen had been analyzed.