The iron sulfate Na3Fe(SO4)3 studied here has been obtained as a high-temperature (HT) product (~400 °C) from the thermal decomposition of sideronatrite from Sierra Gorda (Chile) having composition Na2Fe(SO4)2(OH)·3H2O. The structure determination was carried out using synchrotron X‐ray powder diffraction. Structural data refined by the Rietveld method, up to Rp = 11.95%, are: space group R3̅, lattice parameters a = b = 13.6231(1) Å and c = 9.0698(1) Å, V = 1457.76(2) Å3, and Z = 6. The structure of Na3Fe(SO4)3 can be described in terms of FeO6 octahedra connected to sulfate tetrahedra by corner-sharing to form infinite chains [Fe(SO4)3]∞, running along c. These chains are joined together by Na atoms to build up a three-dimensional network of strong (Fe-O-S) and weak (Na-O) bonds. The topological relationships of Na3Fe(SO4)3 to the structure of some analog minerals are also discussed.