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Although duplex stainless steels (SS) exhibit good performance in many severe corrosive environments, their corrosion resistance can be hampered by precipitation of chromium (Cr)-and molybdenum (Mo)-rich phases during heat treatments. The influence of aging treatments on intergranular corrosion (IGC) of a commercial 25% Cr-5% nickel (Ni) duplex SS (UNS S32550) was studied. The SS was given aging treatments in the range 773 K to 1,173 K for durations from 6 min to 100 h. Microstructure study of the aged samples indicated the presence of various phases, among them , Cr-rich carbide, secondary austenite, ␣´, and copper (Cu)-rich precipitate. The influence of these precipitated phases on IGC susceptibility of the SS was evaluated by the ferric sulfate (Fe 2 [SO 4 ] 3 )-sulfuric acid (H 2 SO 4 ) and Cu-copper sulfate-(CuSO 4 )-H 2 SO 4 tests. Results indicatedand Cr-rich carbide increased IGC susceptibility greatly, as did aging in the range 873 K to 1,073 K.