The pressure dependence of the crystal structure of Sr 2 Fe 2 O 5 has been studied at room temperature by angle-dispersive synchrotron X-ray powder di4raction and 57 Fe MoK ssbauer spectroscopy using diamond anvil cell techniques. Between 11 and 14 GPa the low-pressure brownmillerite-type structure with an equal number of octahedrally and tetrahedrally coordinated Fe 3Ψ sites is transformed into a tetragonal perovskite-like structure. The MoK ssbauer spectra of the high-pressure phase reveal two subspectra with an intensity ratio of about 3:1. The MoK ssbauer parameters are consistent with two 5ve-coordinated Fe 3Ψ sites di4ering in the degree of structural distortion of the FeO 5 polyhedra. Laser annealing of the high-pressure phase at 15 GPa induces a transformation from the tetragonal perovskite into an orthorhombic phase that is isostructural with Sr 2 Mn 2 O 5 . This structure consists of a network of corner-sharing FeO 5 square pyramids. The coordination number of the Sr 2Ψ ions has increased from 8 in the brownmillerite structure to 10 in the Sr 2 Mn 2 O 5 -type phase.