Numbers of nuclear power plants have been operating for more than 30 years and some of them exceeding 40 years in Japan. In these ageing plants, fatigue evaluation has a significant measure in assuring the plant reliability. The environmental fatigue in light water reactors, which was first recognized in the 1980's in Japan, has been drawing attention worldwide because it may cause remarkable effects on the life of important components. The Japanese nuclear industries developed the world's first practical methodology to evaluate environmental fatigue and it has been utilized in plant life management (PLM) technical evaluation. The Japan Society of Mechanical Engineers (JSME) issued the codes regarding environmental fatigue, JSME S NF1-2006, and has redrafted them incorporating the latest knowledge in 2009. This paper introduces a few examples of environmental fatigue evaluation, which was performed using the JSME codes as a part of PLM evaluation for Japanese PWR plant.