Nickel based alloy is used for light water reactor power plant components such as penetration nozzles and butt weld nozzles of reactor vessels. In recent years, stress corrosion cracking (SCC) occurred at the nickel based alloy weld joints of the power plants in Japan and foreign countries. Integrity of cracked components is evaluated according to the flaw evaluation procedure prescribed in the maintenance rule issued by The Japan Society of Mechanical Engineers (JSME). However, the latest version (2008 edition) of Rules on Fitness-for-Service for Nuclear Power Plants of JSME maintenance rule does not provide the flaw evaluation procedure for nickel based alloy components. The working group of flaw evaluation of JSME code and standard committee have been involved in establishing the flaw evaluation procedure from 2008 and three code cases were published by JSME. This paper introduces the brief contents of the code cases for flaw evaluation for nickel based alloy components.