The heat of vaporization of water in agricultural products is an important factor to design the drying equipment. The thermal properties can be calculated by an equation that derived easily form ERH/EMC equation by the Clausius-Claperton thermodynamic theory. The modified-Oswin equation can serve as the good model to obtain the heat of vaporization of corn kernel, rough rice and soybeans. The empirical model derived from the Othmer method gives the larger deviation.