PBS soluble- and insoluble-extracts form silkworm eggs were analysed by native-PAGE and SDS-PAGE. During the embroyonic development, soluble proteins which are mainly composed of ESP, vitellin and 30K proteins showed similar degradation pattern in both electrophoretic analyses. Several peptides which seemed to be intermediated forms of yolk proteins were detected in latter part of embryogenesis, while a protein band newly appeared in one day elapsed after acid treatment. When insoluble extracts from silkworm eggs were analysed with SDS-PAGE, several peptides were detected at the later stages of the embryonic development, and newly hatched larvae. These peptides are considered to be structure proteins for embryonic morphogenesis.