The new iron layered oxysulfate ST4Fe2.5O7.25(SO4)(0.5) has been prepared by a solid-state reaction in closed ampules into the form of ceramics and single crystals. Its atomic structure has been solved by means of spectroscopy, diffraction techniques, and high -resolution electron microscopy. ST4Fe2.5O7.25(SO4)(0.3) is a layered structure that derives from the Ruddelsden-Popper (RP) phases with the layer stacking sequence SrO/SrFeO2.5/SrFe0.5(SO4)(0.5)O-1.25/SrFeO2.5. Within the mixed Fe3+/SO42- layer, the sulfur atoms are slightly shifted from the B site of the perovskite and each sulfate group shares two corners with iron pyramids in the basal plan without any order phenomenon. The electronic conductivity is thermally activated, while no ionic conductivity is detected.