The austenite stability and deformation behavior of 15Cr-15Mn-4Ni based austenitic stainless steels alloyed with C or N are studied. Stability of austenite against martensitic transformation was enhanced with increasing C or N content, while N was a more effective element at an equivalent concentration. With the addition of interstitial elements, both yield and tensile strengths increased. The more pronounced effect of N than C on the yield strength was likely to be due to the formation of short range ordering (SRO) and its higher binding energy with dislocations. The strain hardening behavior was described by classifying the deformation regime into two parts. At low strain, short-range obstacle was a main governing factor, while strain-induced martensitic transformation and dislocation interaction controlled the strain hardening at high strain. The difference between C and N on strain hardening at low strain arose from the existence of SRO which induced the formation of planar slip in N containing alloys. On the other hand, the difference in strain hardening behavior at high strain was attributed to the difficulty of SRO recovery in N containing alloys and a larger increase of SFE by N addition in comparison with C.