The effect of water jet peening (WJP) on the improvement of stress corrosion cracking (SCC) and fatigue strength was verified by performing SCC and fatigue tests. The SCC specimens employed were sensitized type 304 stainless steel simulating the heat affected zone in welded metal. The creviced bent beam (CBB) type SCC test was performed in high temperature water using the smooth and pre-cracked specimens. WJP remarkably improved the susceptibility of SCC for the smooth specimen, and cracks were not initiated when the applied strain was less than 0.3%. WJP was also confirmed to prevent SCC for the pre-cracked specimen. In the fatigue tests both smooth and pre-cracked plate specimens were subjected to cyclic bending loads in air at room temperature. The fatigue strength of smooth and pre-cracked specimens at a fatigue life of 10⁷ cycles was increased by 1.1 and 2.4 times, respectively, in comparison with that of non-WJP specimens. This means that WJP was much more effective for the pre-cracked specimens. CBB and fatigue tests show that WJP is an effective technique for preventing SCC in the structural components of power plants.