Peroxiredoxins (Prxs) are a ubiquitous family of proteins that play important roles in insects in protection against oxidative stress through the detoxification of cellular peroxides. Here, we describe the cloning and characterization of a Prx4 cDNA of the silkworm Bombyx mori (BmPrx4). The BmPrx4 gene has an open reading frame of 744 bp encoding 248 amino acids and a conserved motif, VCP, involved in its presumed redox functions. The heterologously expressed proteins of the gene in Escherichia coli showed antioxidant activity, removed hydrogen peroxide and protected DnA. Western blotting analysis showed the presence of BmPrx4 in the haemolymph, suggesting that the protein is secretable. Moreover, BmPrx4 was expressed at all developmental stages. The expression level of BmPrx4 was relatively low during the feeding stage but high at the wandering stage. BmPrx4 was induced by quercetin or temperature stress. Immunohistochemical analysis revealed that BmPrx4 is present in the brain, neurones and olfactory organ of the head in silkworms. Overall, our results indicate that the expression profile of BmPrx4 correlates well with protection from oxidative damage. Our data provide clues for the development of control technology for agricultural and forestry pests as the silkworm is a representative of lepidopteran pests.