This paper describes the low cycle fatigue behavior of 1Cr-1Mo-1/4V and SUS304 cruciform specimens in wide range biaxial stress conditions of -1.0≤φ≤1.0 at high temperatures, where φ denotes the ratio of the minimum principal strain to the maximum principal strain existing on the specimen surface. The detailed description of the newly developed biaxial fatigue testing machine was made, and the biaxial test results were discussed in connection with the biaxial low cycle fatigue parameter. The COD and ther Γ*-plane parameters were most appropriate to express the biaxial fatigue behavior. Also the X-ray diffraction was made in order to examine the damage in biaxial stress states.