Interleukins are reported to be valuable immunostimulants in enhancing the immune efficiency of conventional vaccines. In this study, the effect of expression of interleukin 8 (IL-8) on the immune response of ducks to avian influenza vaccine was investigated. The results showed that the serum antibody titer, lymphocyte transformation efficiency and serum interferon gamma (IFN-γ) level of ducks injected with avian influenza vaccine along with a plasmid expressing duck IL-8 were higher than those of ducks injected with conventional immunostimulant Astragalus polysaccharide (APS) or empty plasmid. Therefore, the duck IL-8 may be used as a good immunostimulant to enhance the immune efficiency of avian influenza vaccine in ducks.