SrFeO3-δ with a tetragonal or orthorhombic perovskite structure at room temperature unliteratures on the structural phase transition behaviors because the specimens with a homogeneous and well-controlled amount of oxide-ion vacancies had not been prepared. In this account, the development of the preparation method of homogeneous SrFeO3-δ with a controlled oxygen content using thermogravimetric data is described. Using thus prepared dergoes structural phase transition to cubic perovskite with a random distribution of oxide-ion vacancies at an elevated temperature. The cubic phase attracts much interest as an oxide-ion and hole mixed conducting material; however, there were contradictions in specimens, the miscibility gap between the tetragonal and orthorhombic phases and their structural phase transition behaviors of the both phases are clarified for the first time. The effect of the structural phase transitions to the cubic phase on thermal expansion and electrical conducting properties is also elucidated.