H9N2 avian influenza viruses (AIVs) have become increasingly prevalent in domestic ducks. To our knowledge, this is the first report of a DEV-vectored vaccine providing robust protection against both DEV and H9N2 AIV virus infections in ducks. Moreover, a single dose of 10 3 TCID 50 of rDEV-∆UL2-HA induced solid protection against lethal DEV challenge and completely prevented H9N2 AIV viral shedding. In vivo tests further showed that the insertion of the HA gene in place of the UL2 gene did not affect the immunogenicity of the virus. One-step growth analyses showed that the HA gene insertion had no effect on viral replication and suggested that the UL2 gene was nonessential for virus growth in vitro. In this study, we constructed a recombinant DEV, rDEV-∆UL2-HA, inserting the hemagglutinin (HA) gene from duck-origin H9N2 AIV into the UL2 gene by homologous recombination. Duck enteritis virus (DEV) may be a promising candidate viral vector for aquatic poultry vaccination. As ducks play an important role in the maintenance of H9 viruses in nature, successful control of the spread of H9 AIVs in ducks will have significant beneficial effects on public health. H9 subtype avian influenza viruses (AIVs) remain a significant burden in the poultry industry and are considered to be one of the most likely causes of any new influenza pandemic in humans.