Abdominal-A (adb-A) is a key gene in the development of insects. To understand its function in the silkworm, we cloned 1193 bp of the abd-A gene of Bombyx mori (Bmabd-A), including the complete coding sequence and part of the 3' untranslated region sequence. Bmabd-A has at least three mRNA splice variants with coding sequences of lengths 1032, 1044 and 1059 bp, encoding 343, 347 and 352 amino acids, respectively. Each splice variant of Bmabd-A has three exons and differs only in second exon size. Bmabd-A was expressed at low levels in unfertilized eggs, but increased gradually in fertilized eggs after laying 22 h. Bmabd-A expression decreased in ant silkworms (newly hatched silkworms). After RNA interference for Bmabd-A, the embryos had two mutant phenotypes, either completely or partially absent abdominal feet from the third to sixth abdominal segments, suggesting that Bmabd-A is responsible for normal development of the third to sixth abdominal segments during embryonic development.