DSC measurements revealed that the C-GL series except for 5-OH-C16GL (7) has crystal polymorphism. There were three types of crystals: type I crystals precipitated by rapid cooling, type II crystals precipitated by heating, and type III crystals precipitated by using organic solvents. Among the C-GL series, C10GL is liquid at room temperature, but when it was solidified by rapid cooling and then slowly heated, an exothermic peak, type II crystallization peak, was observed near 0°C. This is cold crystallization due to C10GL's heat storage properties, which is expected to have an icemelting effect. In the C-GL series, the exothermic temperature due to cold crystallization (type II crystallization) varies depending on the length of the fatty acid. When used as a heat storage material, the exothermic temperature can be controlled by simply changing the length of the fatty acid, and we speculate that it can be used as a heat storage material that suits the purpose. Furthermore, FT-IR measurements of each crystal polymorph indicate that intermolecular hydrogen bonds are formed by carbonyl groups as the crystal polymorph shifts from I to II and III. This is the reason for the increase in melting point. Furthermore, correlation with XRD measurements revealed that a lamellar structure is formed in type III crystals. Since there is no crystal polymorphism in 5-OH-C16GL (7), fatty acid binding to all hydroxy groups of 1,4-GL is required to create the crystal polymorphism.