The effect of melt crystallization on inorganic hydrate for purification of crystals containing liquid and solid impurities was investigated. Melt crystallization is generally applied to purify organic crystals. In the case of inorganic crystals, it is cost-ineffective because of the higher melting point. However, some inorganic crystals, i.e., hydrate crystals, can be applied to melt crystallization because of the lower melting point. Hydrate crystals containing impurities were prepared and melt crystallization was carried out to investigate the purification mechanism on inorganic crystals. Liquid impurity in target crystals was removed by sweating and washing with melt. Solid impurity was also separated with melt flow, supported by mixing operations. It was considered that the purification mechanism is differently dependent on the state of impurity.