The nucleotide sequences containing an entire genomic region and 5' upstream region of Antheraea yamamai fibroin gene have been determined. The gene consists of an initial exon encoding 14 amino acids, an intron (150 bp), and a long second exon coding for 2641 amino acids. The fibroin coding sequence shows a specialized organization with a highly repetitive region flanked by non repetitive 5' and 3' ends. Northern blot analyses confirmed that fibroin gene is actively expressed in the posterior silk gland of the final instar larvae of Antheraea yamamai.