Abstract: The thermally aged 304 stainless steel specimens were characterized for their degree of sensitization (DOS) by double-loop (DL) electrochemical potentiokinetic reactivation (EPR) method. Then the chromium depletion zones of these tested specimens were observed by metallographic microscopy. The results show that chromium depletion zones were first in the shape of points, then expanded to chains with the increase of DOS, and finally distributed near the grain boundaries in the form of mesh.