This paper describes a successful transplantation of the silkworm at the pupal stage. The biological effect after the implantation of the ovary into the male pupa was investigated, and the period during which transferance of vitellogenin to the ovary via the blood occurred was identified as the pupal stage. The result of the experiment was as follows; for the 2-hr aged male and female pupa, it was most suitable to do the transplantaton after low temperature treatment of the pupae; after the ovary was implanted into the male pupa, the rcipient developed very well, the rate of emergence reaching 82. 5 % - 1 00%, Mature eggs formed inside the ovary of the male pupa, though there were some changes in size, weight, protein content, nuclec acid content and ultrastructure of the eggs. After parthenogenesis treatment, 14. 2% -16. 8% of the eggs inside the male pupa developed into early embryos and it should be possible to have progenies if further study is conducted.