Stress corrosion cracking (SCC) was investigated by spectral analysis of corrosion potential signals. Caustic cracking of carbon steel (S10C) and SCC of stainless steel (SUS304) in various chloride solutions were studied. The marked change of the power spectral density (PSD) in the frequency domain was observed in the vicinity of 5mHz for caustic cracking of carbon steel and in the frequency range from 10 to 100mHz for SCC of stainless steel. It was also observed that the corrosion potential signal in 20%NaCl+1%Na₂Cr₂O₇ solution was bigger than in 42%MgCl₂ solution or 60%CaCl₂ solution for SCC of Stainless steel. By comparing PSD with the changes of elongation and corrosion potential, the following conclusion was obtained: the increase of PSD might be related to the breakdown of passive film and the generation of cracks for caustic cracking of cabon steel, while its increase might be attributed to the localized change in the passive film for SCC of stainless steel.