The paper considers phase equilibria in the subsolidus region of the GdFeO₃-SrFeO_3-δ system in air. By using X-ray powder diffraction, SEM/EDS, and Mössbauer spectroscopy, a GdFeO₃-SrFeO_3-δ phase diagram was constructed in the 1300–1500 °C temperature range. The samples of Gd_1-xSr_xFeO_3-α for this study were synthesized by solid-phase chemical reactions. The study of phase equilibria in the GdFeO₃-SrFeO_3-δ system showed the presence of three areas, that is, of solid solutions based on the strontium-poor GdFeO₃ orthorhombic phase, of the strontium-rich SrFeO_3-δ cubic phase, as well as of an intermediate region in the mixture of these phases. The miscibility gap width (Δx) decreases from 0.54 to 0.35 with an increase in temperature from 1300 to 1500 °C.