In this study, to obtain a more accurate analysis of the temperature in microwave coagulation therapy (MCT) for liver cancer, the water content ratios of dehydrated liver tissue and the dependencies of the dielectric and thermal constants of the tissue on the water content ratios were investigated in tissue heated at 2.45GHz. Swine liver tissues were heated and dehydrated under various conditions, and the water content ratios and dielectric and thermal constants were measured. The results indicated that the water content ratio of the tissue depended on the heating temperature and that the dielectric constants (relative permittivity and electrical conductivity) and thermal constants (specific heat and thermal conductivity) of the dehydrated tissues strongly depended on the water content ratio. Based on these results, numerical analyses of the electromagnetic field and temperature inside the liver tissue heated with a coaxial-slot antenna were conducted. Incorporating information on the water content ratio improved the accuracy of temperature calculations in MCT.