Antheraea yamamai vitellin was purified from matured eggs by polyacryamide gel electrophoresis, also stage dependent appearance, immunological comparison and relative content of the protein were investigated. 1. Vitellogenin, the precursor of vitellin, was first detected in the larval hemolymph at the late spinning stage by polyacrylamide gel electrophoresis and immunoelectrophoresis. 2. The electrophoretic mobility of the vitellin was identical with that of Bombyx mori and of Bombyx mandarina. However, the specific antiserum against A. uamamai vitellin did not react with either that of Bombyx mori or Bombyx mandarina in immumo-diffusion test. 3. Relative content of A. yamamai vitellin to the total soluble egg protein was 46.0 percent and did not change till eight days after oviposition. But the content started to decline from ten days after oviposition and was negligible in the five or serventeen month old eggs.