Lattice dynamical calculations of ice VIII have been made by using a slightly modified set of force constants obtained recently for ice Ih (model of two types of hydrogen bonds, Li and Ross). The only weak hydrogen bond interaction between the water molecules in ice VIII was assumed according to its crystal structure, and in addition, an interaction between the two interpenetrated sublattices in ice VIII structure was included. The calculated results for H2O and D2O ice VIII we in reasonable agreement with the measured inelastic neutron-scattering spectra.