We constructed a bacterial artificial chromosome (BAC) library from the large white butterfly, Pieris brassicae (L.) (Lepidoptera: Pieridae), which composed of 15,360 clones with an average insert size of 103 kb. We designed 39 degenerate oligonucleotide primer pairs and cloned the PCR products for sequencing. From these plus pierisin data, we designed single tagged sequence primers and selected 40 BAC clones using a 3-step PCR protocol. Additional 40 BACs were sequenced to improve identification of P. brassicae BACs carrying orthologs of the silkworm, Bombyx mori (L.) (Lepidoptera: Bombycidae). Among 34 BAC clones containing multiple B. mori orthologs, sequences in 27 BACs correspond to a block (less than 1 Mb) of every B. mori chromosome. While orthologs in 5 BACs showed collinearity to each B. mori chromosome with a distance (1.4-6.8 Mb), orthologs in two BACs corresponded to genes in more than two different B. mori chromosomes.