The mock-up specimens containing such natural flaws as fatigue cracks and stress corrosion cracking are of great use for qualifying examination and training of non-destructive inspection personnel. In this paper a few methods newly developed for introducing fatigue cracks and stress corrosion cracking into mock-up specimens are described. In order to have fatigue crack, an EDM notch was first machined in a specimen as a starter of a fatigue crack in advance. A fatigue crack started from the notch by one of two methods, repeated mechanical stress or thermal stress cycling. In the former method, repeated mechanical stress cycling generated by hydraulic cylinder was applied locally to the notch, while in the latter method stress cycling was developed around the notch by the repetition of high-frequency heating and water-cooling. These methods were found to be applicable to introduce fatigue crack in complicated structural details such as a welded joint between a nozzle a shell plate in a vessel and its vicinity, and a nozzle corner. The size and shape of an expected fatigue crack can be controlled by the size and shape of the pre-machined EDM notch and by in-process monitoring using an electronic crack depth meter and UT examination. To produce stress corrosion cracking in a mock-up specimen, an intended are to produce the cracking was first covered by graphite fiber wool, and the specimen was subjected to tensile loading in an elevated temperature and high pressure water environment. This method was found to be available to develop stress corrosion cracking in relatively short time in a large scale specimen, outer diameter up to 650 mm and overall length of up to 1,000 mm.