Athetis lepigone was a new lepidopteran pest and caused severe damage to maize crops in China. We have detected that Cry1Ac protoxin and toxin were highly active against the larvae of A. lepigone. However, there is no report about the mode of action of Bt Cry1Ac toxin against this pest until now. A 110 kDa APN5 protein from BBMV of A. lepigone was identified as the binding receptor of Cry1Ac toxin using Ligand blotting. The Cry1Ac receptor APN5 was cloned from A. lepigone larval midgut mRNA and named as AlAPN5 (GenBank accession no.: KU950745). AlAPN5 had a GATEN motif and been classified to Class 5 APNs. 79.2% reduction in mortality was observed when A. lepigone larvae were injected with siRNA of the AlAPN5 gene and treated with Cry1Ac toxin. These data demonstrate that AlAPN5 is a putative functional receptor and maybe the only receptor of Cry1Ac in A. lepigone.