To develop a fatigue design curve of cast stainless steel CF8M that has been used in piping material of nuclear power plants, a low cycle fatigue tests were conducted in the environment of a pressurized water reactor at 15 MPa and 315 degrees C. Cylindrical solid fatigue specimens were used for the strain-controlled environmental fatigue tests. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitudes at 0.04%/s strain rate. This paper focuses on the characteristics of the cyclic strain hardening effect caused during environment fatigue tests of the CF8M cast stainless steel. The process and method of correcting fatigue test data in this paper would be so useful to produce reliable data of environmental fatigue curves for the material in operating condition of high pressure and high temperature water environments. (C) 2009 Elsevier Ltd. All rights reserved.