The structure of rhombohedral (R3) iron(III) tris[dihydrogenphosphate(I)] or iron(III) hypophosphite, Fe(H2PO2)3, has been determined by single-crystal X-ray diffraction. The structure consists of [001] chains of Fe3+ cations in octahedral sites with -3 symmetry bridged by bidentate hypophosphite anions.