The thermal properties of liquid silk obtained from the domesticated silkworm (Bombyx mori), the mutant domesticated silkworm (Sericin cocoon silkworm, Nd-s), and four wild silkworms (Samia cynthia ricini, Dictyoploca japonica, Antheraea pernyi and Antheraea yamamai) were investigated by differential scanning calorimetry (DSC). The weak endothermic peak in the DSC curves for the liquid silk of the domestic silkworm corresponded to the breaking of hydrogen bonds in the a-form of fibroin. The process of crystallization of the liquid silk differed between domestic and wild silkworm. The starting temperature of transition for the liquid silk of the domestic silkworm was calculated.