To develope the genetic source of oak wild silkworm, Antheraea yamamai, the cDNA library was constructed with poly A+ mRNA isolated from posterial silk gland of fifth instar larvae. Titer of the cDNA library was about 5.1$ imes$105 pfu in total. We presumed that the titer covered almost all transcripts existed in Antherea yamamai. From cDNA library of Antheraea yamamai, fibroin heavy chain gene, which is specifically expressed from posterial silk gland of Antheraea yamamai, was screened using oligonuclotide probe specific to alanine rich motif of fibrin heavy chain gene of Antheraea pernyi. As a result, fibroin clones isolated from 5$ imes$104 plaques showed the highest homolgy (95%) with that of Antherea pernyi in nucleotide of Anthereaea yamamai and Bombyx mori shows that there is no homologous sequence in the 3+ partial 채야후 region Genomic southern hybridization suggested that one copy is present. Northern hybridization showed that fibroin transcript was approximateely 9 kb in length.