The complex perovskite with composition Ba3FeWO9 (BFWO) has been synthesised, and the evolution of nuclear and magnetic structures with temperature has been investigated by neutron powder diffraction. It was shown that at room temperature this compound adopts the 6H-perovskite structure, space group P6(3)/mmc (a = 5.7584(2) Angstrom, c = 14.1019(9) Angstrom), in which the cation sites within the face-sharing octahedra are occupied by Fe and W cations and those within the corner-sharing octahedra are occupied by Fe exclusively. The magnetic diffraction peaks were registered at low temperatures and a possible model for the magnetic structure was proposed in accordance with the ferrimagnetic properties of BFWO. The magnetic structure can be described as an array of ferromagnetic layers of Fe moments along the c-axis, and adjacent layers coupled anti ferromagnetic ally. Structural and magnetic features of this compound are discussed and compared with those of other quaternary oxides adopting the 6H-perovskite structure. (C) 2004 Elsevier Ltd. All rights reserved.