To generate monoclonal anti-idiotypic antibodies (mAb2) against avian influenza virus subtype H9 (H9 AIV),BALB/c mice were immunized with purified chicken anti-H9-AIV IgG and the splenocytes of immunized mice were fused with myeloma cells NS-1. Hybridoma cells were screened by indirect enzyme-linked immunosorbent assays with both chicken and rabbit anti-H9-AIV IgG as coating antigens. One hybridoma cell clone secreting monoclonal antibody against idiotypes shared by both chicken and rabbit anti-H9-AIV IgG was established. Experiments demonstrated the mAb2 was able to inhibit the binding of hemagglutinin to anti-H9-AIV IgG and to induce chickens to generate hemagglutination inhibition antibodies, indicating this anti-species-sharing-idiotypic antibody bore the internal image of hemagglutinin on avian influenza virus. Cellular & Molecular Immunology. 2005;2(2):155-157.