[Objective] In order to provide new clues for further understanding of the immune defense mechanism of silkworm, theexpression pattern of antibacterial peptide genes were explored in silkworm during the molting stage. [Method] Using the silkworm larvae of the fourth molting 0, 12, 24 hours and the newly molted fifth instar as the experimental materials, the antibacterial activity of hemolymph was measured by bacteriostatic curve method and the expression of antibacterial peptide genes was detected and analyzed by the real-time fluorescent quantitative PCR. [Result]The results showed that the hemolymph of the fourth molting 0, 12, 24 hours and the newly molted fifth instar did not have antibacterial activities against Staphylococcus aureus, while the hemolymph of the fourth molting 12 and 24 hours had obvious bacteriostatic effect on Escherichia coli. It indicated that the hemolymph of the silkworm had selective antibacterial activity during the molting stage. During the different development stage from the fourth molting to the newly molted fifth instar, the expression levels of Lebocin3 and Moricin did not change, the Attacinl gene was up-regulated only at the fourth molting 24 hours, and the expression of CecropinB6 and Gloverinv2 was gradually decreased, showing a downward trend in expression, while the expression levels of Enbocin2 and DefensinB gradually increased, showing an up-regulated expression trend. [Conclusion]It is suggested that the expression patterns of seven antibacterial peptide genes in silkworm are not consistent at the molting stage of Bombyx mori, and the Attacin1, Enbocin2 and DefensinB may play a certain role in the immune defense during this period. [ABSTRACT FROM AUTHOR]