The thermodynamic quantities of fusion for long-chain symmetrical ketone homologues were studied by DSC measurements. The carbon numbers in the chain measured were from 23 to 63. A heat-flux-type DSC was used because of its relatively high sensitivity at slow scanning rates. In addition to these, the heat capacities of ketones in the solid and liquid states were measured, for which sapphire was used as a standard material. Although the symmetrical ketone have almost the same crystal system and lattice constants as those of odd n-alkane crystals, known as model compounds for polyethylene, ketones have no high-temperature modifications. In view of these points, the purpose of this paper is to examine the linearity of the entropies of fusion, Delta S-m(T-m(0)) at the equilibrium melting temperature T-m(0) for n = infinity, calculated using the DSC data measured with ketones, also considering the contributions of another entropy term, R ln n as pointed out by Flory and Vrij in 1963. It is concluded that not only the heats of fusions, Delta H-m(T-m(0)), but also Delta S-m(T-m(0)) satisfactorily indicate a linearity. Furthermore, it seems reasonable to conclude that the validity of the term R ln n is not clearly shown in these analyzed results.