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In the present work, the structure and phase composition of a high nitrogen austenitic steel were studied in dependence on the aging temperature from 600°C to 800°C. Age-hardening in the regimes 600°С, 5 h., 700°С, 0,5 h., и 800°С, 10 min. is accompanied with a decomposition of a [delta]-ferrite into a [sigma]-phase and an austenite, and simulteneous discontinuous decomposition of austenite with the formation of Cr[2]N-cells along grain boundaries and cells of austenite depleted by interstitials. The decomposition of [delta]-ferrite and austenitic grains occurs faster with increase in age-hardening temperature. Along with discontinuous decomposition of austenitic grains, there is a homogeneous (continuous) nucleation of Cr[2]N nitrides in those austenitic grains, which have not underwent discontinuous decomposition at the initial stages of aging.