The purpose of this study is to investigate environmental effects on low cycle fatigue crack growth of SUS316. Low cycle fatigue test and periodical observation on inner surface of a hollow specimen was conducted by developing new type of replica observation. The crack growth in PWR environment was measured and the investigation of environmental effects on crack growth was conducted. Crack initiation rate of fatigue test in PWR environment is faster than in air condition. Crack initiation is estimated to be dominant in crack growth both in environmental fatigue and Stress Corrosion Cracks (SCC) condition. Consideration of crack initiation in earlier period of fatigue test, acceleration of crack growth rates in PWR environment and coalescence of cracks by short initiation time and high density of cracks is necessary to quantify environmental effects.