A new layered alkali-transition metal oxide was prepared by the solid state reaction of LiCoO2 and Na0.7CoO1.96 in air at 850-degrees-C. Its chemical formula is Li0.43Na0.35CoO1.96 as determined by atomic absorption spectrophotometry and high resolution neutron powder diffraction. X-ray and neutron diffraction data of the material were indexed using the hexagonal P6(3)mc space group with lattice parameters a=2.839(4) angstrom and c=20.36(3) angstrom. High resolution neutron powder diffraction data of the layered metal oxide were analysed ab initio to reveal a structure with alternating lithium and sodium layers intercalated between octahedral sheets oxide (CoO6). The lithium ions are sited within an octahedral oxygen framework whereas the sodium ions are within a trigonal prismatic oxygen environment (between the CoO6 layers). The sodium ions occupy two available sites unequally (the probability of finding sodium ions at one site being approximately twice that for the other site) due to the influence of second nearest neighbour cobalt ions.