The lattice-dynamical properties of the intermediate oxide of tin (IO) have been investigated over the temperature range 80–295 K. The logarithm of the recoil-free fraction varied linearly with temperature. However, a Debye model does not give a good account of this dependence. By comparison with the other oxides of the Sn-O system, the recoil-free fraction for tin atoms with 2+ and 4+ oxidation states of the IO were estimated. At room temperature, they are 0.463 and 0.323 for 4+ and 2+ states respectively.