Bursal pentapeptide (BPP)-(III-V) are peptides isolated from the bursa of Fabricius (BF). The peptides´ adjuvant activities were evaluated in mice immunized with the H9N2 avian influenza vaccine. The results showed that BPP-IV did not promote humoral or cellular immune responses. BPP-III had no effect on antibody production, but increased populations of CD3+ and CD8+ T cells, CTL levels and proliferation activities of splenic T-lymphocytes. BPP-V increased the level of antibodies (HI, IgG and its subtype IgG1) and the cytokine IL-4, as well as the ratio of CD3+ T cells and its subsets CD4+ and CD8+ T cells, BPP-V also increased CTL level and promoted the proliferation activity of T- and B-lymphocyte. Furthermore, in animal challenge experiment, BPP-III and BPP-V reduced viral RNA copies and viral titers, and reduced inflammatory cell infiltration. In summary, BPP-IV did not have an effect on specific immune responses, therefore it could not reduce pathological damage in mice lungs; BPP-III provided resistance to the antigen through the cell-mediated immune response; BPP-V enhanced both humoral and cellular immune responses, and therefore provided protections against the H9N2 avian influenza virus (AIV). Altogether, BPP-III and BPP-V could be adjuvant candidates for the H9N2 avian influenza vaccine.