Two forms of LiNbWO 6 were previously described : a trirutile phase and an other form claimed to be isostructural with LiNbO 3. The trirutile phase, that we call α-LiNbWO 6, transforms in the other form, β-LiNbWO 6, at 820°C which in turn decomposes at 870°C into NbW 2O 6 and Li 2WO 4. The structures of α and β-LiNbWO 6 are solved from powder diffraction data analysed by a Rietveld method. α-LiNbWO 6 adopts a new quasi-ordered trirutile structure (s.g. P4̄2 1m, Z = 2. a = 4.6819(2) A, c = 9.2757(5) A, R r = 0.0515, R p = 0.0974, R wp = 0.1177 (X-ray data) and R r = 0.0375, R p = 0.0822, R wp = 0.0890) (neutron data)). β-LiNbWO 6 exhibits the LiNbO 3 structural type where Nb and W are completely disordered (s.g. R3c, Z = 3, a = 5.1562(9) A, c = 13.664(3) A, R I = 0.0426, R p = 0.1028, R wp = 0.1029).