The crystal structure of scainiite, Pb14Sb30S54O5, has been solved from single-crystal X-ray data and refined to an R index of 8.9 % based on 3703 unique reflections. The structure is monoclinic C2/m, with cell parameters a 51.996(8), b 8.148(1), c 24.311(4) Å, β 104.09(1)°, V9990(10) Å3, and with Z = 4. The structure analysis was essential in determining the position of oxygen atoms in a special double-ribbon, Sb8(Pb,Sb)2S10O5, directly related to the structure of kermesite, Sb2S2O. The general organization of the structure can be described according to the general principles developed by Makovicky (1993) for complex sulfides related to the PbS and SnS archetypes. This structure falls into the group of “pure rod structures” (zinkenite group), and is an expanded homologue of cyclic hexagonal Ba12Bi24S48. The expansion of the parent structure is obtained by shearing along a zig-zag surface, that creates lozenge shaped spaces in place of the original hexagonal channels, and filling these spaces by the kermesite-type fragments.