In our previous study, we found that small heat shock proteins (HSPs) in Antheraea pernyi have an important role in response to biotic stress. In order to investigate more function and mechanism of HSP in insect immunity, we report the cloning of Hsp20.1 from the Chinese oak silkworm A.pernyi (Aphsp20.1). The open reading frame of ApHSP20.1 encodes 187 amino acid protein, sharing 75% amino acid sequence identity with the other ApHSP. And phylogenetic analysis reveals that ApHSP20.1 is closely related to other known lipidopteran HSP20 genes. A quantitative real-time PCR (RT-qPCR) analysis indicated that Aphsp20.1was expressed in all tested tissues and was induced by exposure to the microbes Escherichia coli and Micrococcus luteus.Notably, the recombinant ApHSP20.1 protein exhibited significant antimicrobial activity.Taken together, these results suggest that ApHSP20.1 might play an important role in the response to biotic stresses and in immune reactions.