Crack initiation mechanism of 18Cr-8Ni stainless steel containing Cu in H2SO4 solution was studied in terms of activation energy for the initiation. The initiation was detected by photo-microscopical observation of specimen surface tested in the temperature range 50 to 90°C at stresses from 75 to 300 MPa. The apparent activation energy was either about 17 or 86 kJ/mol depending on the stress level and the temperature. The discussion lead to the conclusion that the initiation stage is a series of a mechanical slip process of the crystal planes and a dissolution process of resultant emergent steps.KEY WORDS: activation energy, initiation mechanism, stainless steel, stress corrosion cracking, sulfuric acid solution boundaries (A); (4) corrosion grooves parallel to wire axis (m);