Nanocrystalline BaFeO4 was prepared and purified by special measures. Magnetic susceptibility measurements confirmed the existence of Fe(VI). X-ray diffraction studies indicated that they have an orthorhombic unit cell with space group Puma and lattice parameters a = 0.8880 nn, b = 0.5512 nm, c = 0.7214 nm. High-resolution transmission electron microscopy (HRTEM) and selected area diffraction (SAED) characterization provided further proofs to the accuracy of XRD data. Both the lattice fringe intervals in the HRTEM image and the cell parameters calculated from SAED pattern corresponded well with those resulted from the XRD analysis. (C) 2003 Elsevier B.V. All rights reserved.