In order to evaluate the effects of carbon and nitrogen additions on the stability of austenite, athermal and deformation-induced α'-martensitic transformation behaviors were investigated in type 304 metastable austenitic stainless steels containing 0.1 mass% carbon or nitrogen. Since carbon-added steel has a lower stacking-fault energy (SFE) than nitrogen-added steel, deformation-twin and e-martensite were preferentially formed in carbon-added steel, whereas a dislocation cell structure developed in nitrogen-added steel. Crystallographic analysis using electron backscatter diffraction method revealed that the difference in the deformation microstructure has a significant influence on the growth behavior of deformation-induced α'-martensite. The interface of the deformation-twin and e-martensite completely suppress the growth of α'-martensite, whereas dislocation cell boundaries have little influence on that. As a result, the mechanical stability of carbon-added steel is slightly higher than that of nitrogen-added steel, although the thermal stabilization effect of carbon is much lower than that of nitrogen.