This work describes the investigation of the embrittlement of AISI 304 steel sensitized at 650degreesC by Charpy impact test, comparing two starting conditions: ( 1) mill annealed and machined (MA-M); and ( 2) solution treated at 1050degreesC by 1 h followed by oil quenching (ST). The degree of sensitization for both samples was assessed by Optical Microscopy ( OM), Scanning Electron Microscopy (SEM) and by Double Loop Electrochemical Potentiodynamic Reactivation test. The results showed that MA-M samples undergo more severe and rapid embrittlement than ST ones and a higher kinetics of sensitization due to small strains concentrated in grain boundaries and alpha' martensite phase produced during the machining operations. The martensite phase is found to be quite stable at the sensitization treatment at 650degreesC. The increase of microvoids nucleation at the grain boundaries seems to be the mechanism of embrittlement in the sensitized 304 steel. (C) 2003 Kluwer Academic Publishers.