High temperature low cycle fatigue tests have been carried out on a 55NiCrMoV8 martensitic steel in the temperature range 200° C to 550° C. At all temperatures, the material shows evidence of cyclic softening. Manson-Coffin and Basquin analysis is applied for lifetime analysis. An elasto-plastic kinematic and isotropic hardening model, taking into account the strain path history, was identified using the isothermal LCF tests. Identification methodology is presented and the model validated by comparing experimental and predicted evolution of hysteresis loops during symmetrical and non-symmetrical total strain LCF testing.