Antheraea yamamai vitellin was purified from matured eggs by polyacrylamide gel electrophoresis for characterization of its biochemical properties : molecular weight, sugar and lipid composition, amino acid composition and electron microscopic morphology, etc. 1. A yamamai vitellin was composed of two subunits, large and small, showing different mobility in SDS-polyacrylamide gel electrophoresis. 2. The molecular weight of the vitellin was estimated to be approximately 450,000 dalton and the large and small subunits were 174,000 dalton and 44,000 dalton, respectively. 3. The vitellin seemed to be a glycolipoprotein since it showed a positive reaction to coomassie brilliant blue, sudan black B and PAS staining. Both subunits were similiar in this aspect. 4. Lipid of the witellin reveraled several different types including saturated lipids. 5. When the vitellin was incubated at 7$0^{circ}C$ for 60 minites its apoprotein still cross-reacted to the specific antiserum to the native vitellin. Its sugar components were also detected by PAS staining, but its lipid portion was not detected by sudan black B staining. 6. Its amino acid composition was similar to that of other insects, but its glycine content was peculiarly very high. 7. The vitellin molecule was spherical in shape with a diameter of 14$pm$0.8nm by negatively.