The paper presents the results of research on the microstructure of austenitic creep-resisting TP347HFG steel after longterm service. The tests of the microstructure were performed using SEM and TEM. The identification of precipitates was carried out using selective electron diffraction. It has been shown that long-term service mostly contributes to the processes of precipitation of secondary NbC carbides inside grains and M23C6 carbides on grain boundaries. In the microstructure of the examined steel, also the processes of polygonization and recrystallization of the matrix were revealed.