The rapid outbreak of the highly pathogenic H5N1 avian influenza virus and its transmission to humans have induced world-wide fears of a new influenza pandemic. The most effective method for the reduction of the impact of such a pandemic would be prophylaxis with a safe and effective vaccine, as well as anti-viral materials. In this study, we generated the specific antibodies 'immunoglobulin yolk (IgY)' from ostrich eggs immunized with a full-length glycosylated recombinant H5 protein of the strain H5N1/Vietnam/1203/2004. Using this simple method, abundant specific antibody (about 200 g) against H5 was successfully produced by one female ostrich in a year. The IgY from the immunized ostrich eggs had strong reactivity to the H5N1 virus as well as to H5 proteins. Furthermore, the antibodies strongly inhibited cytopathic effects in MDCK cells and prevented the death of an embryonated chick after a viral inoculation, indicating strong neutralization activity against H5N1 infections. These findings suggest that the neutralization antibody produced by the H5-immunized ostrich is suitable for industrial purposes, such as the development of antibody-binding filters, which can be applied to a mask or to air-conditioners to prevent the influenza pandemic through antigen-antibody reactions. Of note, the mortality rate of chicks inoculated with the H5N1 virus was dramatically decreased with antibody injection. This indicates that ostrich IgY is a potentially effective therapeutic modality for H5N1 infection.