Precipitation behaviors of Nb-contained 316LN austenitic stainless steels during isothermally aging at 650, 750 and 800 °C up to 1000 h have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrolytic extraction experiment. The experimental results show that, long-term thermal aging process introduced signification amount of precipitates both at grain boundaries and on dislocations inside austenitic matrix to Nb-contained 316LN SS. The quantitative calculation of precipitates volume fraction confirmed the sensitive aging temperature was approximate 750 °C. The precipitation behavior of minor phases during Nb-contained 316LN SS different aging treatment was summarized. In Nb-contained 316LN SS aging process, Z-CrNbN phase was the first and predominant nitride phase. Nb element addition into 316LN SS, promoted the formation of σ -FeCrMo and η -Fe 2 Mo phase, restrained the formation of carbide Cr 23 C 6 . [ABSTRACT FROM AUTHOR]