A new quaternary compound, La3Cu2VO9, was synthesized and studied by XRD, TEM and EDS : The phase was found to be stoichiometric and stable in air up 1000 degrees C. From powder XRD data the crystalline phase could be described by a hexagonal. unit cell, with the parameters a(h) = 14.4427(7) Angstrom, c(h) = 10.685(1) Angstrom and cell volume of 1930.15 Angstrom(3). Electron diffraction studies yielded a 4 times larger monoclinic supercell with the parameters a(m) = 14.4427 Angstrom, b(m) = 10.685 Angstrom, c(m) = 52.07 Angstrom, and beta = 106.1 degrees. The valence states of Cu and V are discussed with respect to conducting and catalytic properties.