The intergrowth structure of a zirconium niobium tungsten oxide has been determined by transmission electron microscopy methods. Electron diffraction patterns reveal the parameters of the monoclinic lattice: a = 19.0, b = 3.9 and c = 13.8 Å; β = 93.5°. Additional reflections in higher-order Laue zones indicate the presence of a diagonal glide plane, leading to a larger unit cell. A structure model of composition Zr
n
Nb8−2n
W12+n
O56 (0.5 < n < 1) has been derived from high-resolution lattice images. Alternating slabs of ReO3-type and of tetragonal tungsten bronze structure are intergrown coherently. Two five-membered rings of MO6 octahedra belonging to adjacent tetragonal tungsten bronze subcells are connected by having two octahedra in common. For the first time, this arrangement of double pentagons is observed in a regular structure.