The production of useful quantities of G protein-coupled receptors is a major problem not only for screening of various drug compounds but also in performing structural biology studies. To solve this problem, we investigated the possibility of using transgenic silkworms for the production of these receptors. Using the human mu-opioid receptor gene, we constructed three transgenic silkworm strains that produced mu-opioid receptors. The silkworms expressed significant amounts of the receptor in the fat body and silk gland. The product was evaluated using a saturation ligand-binding assay. The expressed receptor exhibited ligand affinity similar to that of an authentic sample, and the yield from the transgenic silkworm was comparable to that obtained using an Sf9-baculovirus expression system. As the mass rearing of transgenic silkworms has already been established, the silkworms can be adapted for production of large quantities of receptors.