We studied the role of the bursicon gene in wing expansion. First, we investigated its expression at different developmental stages in the silkworm, Bombyx mori. Bursicon gene was expressed at low levels in larvae, high levels in pupae, and low levels again in adults. Then, we injected the double‐stranded bursicon RNA into B. mori pupae to test RNA interference. The level of bursicon mRNA was reduced significantly in pupae, and a deficit in wing expansion was observed in adults. In addition, the differential display reverse transcription polymerase chain reaction (DD‐RT‐PCR) was used to reveal differences in the expression of transcripts in response to the inhibition of bursicon. In conclusion, bursicon plays a key role in the stereotyped behavioral program involved in wing expansion.