To obtain a fundamental information about fatigue properties of materials, hysteresis loop data obtained from the fatigue tests conducted on austenitic stainless steels of SUS 304 and 316 at 288°C, and a nuclear vessel material of SFVV 3 at room temperature, were analysed. And then the cyclic characteristics of hysteresis loops at room temperature and 288°C were compared. The main conclusions obtained are as follows : (1) In the first few cycles at 288°C, austenitic stainless steels SUS 304 and 316 exhibit cyclic hardening and then they transfer to cyclic softening stages after showing the maximum true stress amplitude at approximately 50 cycles. (2) The ratio of plastic strain hysteresis energy per cycle Δ W to the product of true stress range and plastic strain range decreases gradually with increasing number of repetition of strain cycling. (3) The fatigue toughness W_f (kgf · mm/mm³) versus N_c or N_f curves were obtained for some groupes of structural steels at room temperature and austenitic steels at 288°C. (4) The relation between the constants a ₀, and n in the n -th power strain hardening formulae at one half of crack initiation life or failure life are expressed by semilogarithmic formula as follows : log a ₀=2.406 (1/ n ) -1.828