The crystal structure of the spinel LiZnNbO4 has been refined by Rietveld’s analysis of powder X-ray diffraction data. The structure has tetragonal symmetry and the cell parameters are : a = 6.0824(1), c = 8.4035(7) angstrom, space group P4122 (Z = 4). The atomic positions are : Zn (4c), Li (4b), Nb (4a), O1 (8d) and O2 (8d). A different ionic conductivity behaviour for the isostructural spinels LiZnNbO4 and Li2TeO4 is detected and it is discussed on the basis of the mobile ion sites in both compounds.