Oxygen contents in perovskite-structure Fe oxides can change in accordance with the valence states of Fe, i.e., AFeO₃ with Fe⁴⁺, AFeO_2.5 with Fe³⁺, and AFeO₂ with Fe²⁺ (A = Ca and Sr). AFeO₃ has a fully oxygenated simple-perovskite structure, and the unusual high valence Fe⁴⁺ in AFeO₃ is easily reduced to relatively stable Fe³⁺ by releasing oxygen. On the other hand, AFeO₂ has an infinite-layer structure, and the unusual square-planar coordination of Fe²⁺ in AFeO₂ changes to tetrahedral and octahedral Fe³⁺ by incorporating oxygen. Sample weight measurements by thermogravimetry and corresponding phase analysis with synchrotron X-ray diffraction data revealed that the difference in the A-site cation strongly influenced the oxygen release and incorporation behaviors. In ambient air, topotactic changes of AFe⁴⁺O₃ → AFe³⁺O_2.5 ← AFe²⁺O₂ for both A = Ca and Sr can occur by releasing and incorporating oxygen in the perovskite structure frameworks. Nonstoichiometric phases with oxygen vacancies are present between SrFeO₃ and SrFeO_2.5.