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 Aphsp20.1was 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.