The corrosion behaviour of 409 stainless steel oxidized cyclically at various environmental temperatures was studied in the simulated condensate solution of mufflers.The oxidation is accelerated by increasing the temperature from 200 to 400℃.The presence of condensates dipped on the specimen surface may enhance the oxidation process,leading to form defective oxide films and Cr-depletion underlying the films especially at 400℃.Sulfate from the condensate-dipping will give rise to sulfidation during the cyclic oxidation,being detrimental to both the oxidation and corrosion properties of stainless steel.The oxidation lower than 250℃ enhances the passive state of stainless steel while oxidations above 300℃ deteriorate its corrosion resistance,even into active corrosion.The active corrosion through the defects such as cracks and nodules in oxide films may be responsible for the perforation of mufflers.