The possibility of prediction of the solubility parameter from the thermal transition behaviors for PE and iPP was investigated. The molar cohesive enthalpy for crystalline polymers below T_g, which is given by the product of the molar volume and the square of solubility parameter, is given approximately by the sum of the molar heat of fusion, the molar glass transition enthalpy and the molar transition enthalpy due to quasi-crystals in the amorphous regions. These enthalpies could be derived from the thermal transition behaviors.