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DsRNA-degrading enzymes (dsRNases) have been recognized as important factors in reducing RNA interference (RNAi) efficiency in different insect species. However, dsRNases in <i>Plutella xylostella</i> are still unknown. We identified the full-length cDNAs of <i>PxdsRNase1</i>, <i>PxdsRNase2</i>, <i>PxdsRNase3</i>, and <i>PxdsRNase4</i>. Gene expression profile showed that <i>PxdsRNase1</i> was mainly expressed in the hemolymph; and that <i>PxdsRNase2</i> and <i>PxdsRNase3</i> were mainly expressed in the intestinal tract. The expression of <i>PxCht</i> (<i>Chitinase</i> of <i>P. xylostella</i>) in <i>P. xylostella</i> larvae injected with the mixture of dsPxCht (dsRNA of <i>PxCht</i>) and dsPxdsRNase1 (dsRNA of <i>PxdsRNase1</i>), dsPxdsRNase2 (dsRNA of <i>PxdsRNase2</i>), or dsPxdsRNase3 (dsRNA of <i>PxdsRNase3</i>) was significantly higher than that in the larvae injected with the mixture of dsGFP (dsRNA of green fluorescent protein gene, <i>GFP</i>) and dsPxCht; the transcription level of <i>PxCht</i> in the larvae feeding on the mixture of dsPxCht and dsPxdsRNase1, dsPxdsRNase2, or dsPxdsRNase3 was significantly higher than that in the larvae feeding on the mixture of dsPxCht and dsGFP. The recombinant protein of PxdsRNase1 degraded dsRNA rapidly, PxdsRNase3 cleaved dsRNA without complete degradation, and PxdsRNase2 could not degrade dsRNA in vitro. These results suggested that <i>PxdsRNases1</i>, <i>PxdsRNases2</i>, and <i>PxdsRNases3</i> were involved in the dsRNA degradation to reduce RNAi efficiency with different mechanisms.