X-ray diffraction and differential scanning calorimetry (DSC) were carried out to clarify the crystallization mechanism of silk fibroin from liquid silk (native silk fibroin solution), In the course of the evaporation of water from liquid silk, silk fibroin crystallizes when weight loss of water reaches 40% at the temperatures below 120 degrees C, The crystallization occurs 20 min after the specimens are put at above 100 degrees C and 1-3 h at below 100 degrees C, . In the DSC curve of liquid silk of domestic silk Bombyx mori, the alpha-beta transition occurs at 51 degrees C. The crystallization temperatures of wild silk Antheraea yamamai, Antheraea pernyi and Dictyoploa japonica are 59, 67 and 62.5 degrees C, respectively. The exothermic DSC peaks at these temperatures are attributed to the conformational change to the beta-form.