Chicken interleukin 2 (IL-2) is one of important nonmammalian cytokines isolated recently. The influencing of IL-2 on immunogenicity of DNA vaccine was examined using infectious bursal disease virus as a model. The IL-2 cDNA of Xiaoshan chicken and the polyprotein gene of IBDV-ZJ2000 were amplified by RT-PCR, cloned, sequenced and inserted into the control of CMV promoter and enhancer of pCI vector. 14-day-old chickens were vaccinated intramuscularly with DNA vaccine, two weeks later, they were boosted with DNA, and two weeks post boost, they were challenged with virulent IBDV. The results showed that protective responses and neutralization antibody responses of DNA vaccine co-administrated with chicken IL-2 were much higher than those of injected with DNA vaccine alone. Furthermore, the T lymphocyte proliferation response of peripheral blood, thymus and spleen, and the B lymphocyte proliferation response of bursa induced by DNA vaccine can be significantly enhanced by chicken IL-2. These results obviously indicated that chicken IL-2 was a strong adjuvant which can significantly enhance the immunogenicity of IBDV DNA vaccine.