Systematic analyses of the specific heat of rare-earth hexaborides are presented using phonon data. Similarity of phonon dispersion curves at lower frequency is found for the rare-earth hexahorides. By this fact, it becomes possible to deduce unknown phonon dispersion curves. We can calculate the phonon specific heat precisely using phonon dispersion curves. Magnetic entropy is derived for GdB6, TbB6, DyB6, and HoB6, indicating their magnetic ground states which are consistent with a point-charge model developed by K. R. Lea et al. (1962, J. Phys. Chem. Solids 23, 1381). (C) 2000 Academic Press.