The effect of nitrogen on the precipitation characteristics of superaustenitic Fe-22Cr-21Ni-6Mo-(0.3N) stainless steels was investigated by means of X-ray diffraction and microstructural observations such as SEM and TEM. The sigma phase and M_(23)C_6 carbide were recognized` in all specimens regardless of their heat treating condition. In case of nitrogen-free specimen, four phases such as σ, M_(23)C_6, M_6C and χ phases were formed by aging treatment after solution treatment. However, two more nitrides such as Cr₂N and AlN were recognized by long time aging in the nitrogen containing specimen. The addition of nitrogen into superaustenitic Fe-22Cr-21Ni-6Mo steel markedly retarded the coarsening of precipitates and promoted homogeneous distribution of precipitates during isothermal aging. The orientation relationships between the matrix and the precipitates formed during aging treatment were also elucidated.