Abstract: Titre and avidity development of the anti BSA IgY in egg yolk during the immunization period, the influences of pH and (HN 4) 2SO 4 on extraction of IgY from diluted egg yolk and the heterogeneity of anti BSA IgY were discussed. The optimal condition of acidified treatment and salt precipitation were pH5.1 and 2.21mol/L (NH 4)s 2SO 4, respectively. The manifold antibodys with different chromatography behaviors were discovered through immunoaffinity column chromatography or Fe 3 metal chelated affinity column chromagraphy of anti BSA IgY. Experiments show that anti BSA IgY in immune egg yolk probobly exists not only with diversity of avidity or specificity but also with difference of fundamentale structure or physica chemical properties.