Antibacterial peptides' genes are rapidly and transiently expressed on immune stimulation, which is the characteristic of immediate early genes. It implies post-transcriptional regulation is an important pathway in antibacterial peptides' gene expression. In a search of putative post-transcriptional regulatory elements, we found a segment of an AU-rich sequence in 3'-untranslated region (UTR) of drosophila diptericin mRNA. 3'-UTR of diptericin mRNA can be specifically bound with Elav and this binding can be competed with the typical AU-rich element (ARE) of c-fos mRNA. These results suggest that the AU-rich sequence in the 3'-UTR of diptericin mRNA may be a cis-acting element and involved in post-transcriptional regulation.