Immunoglobulin in yolk (Ig Y) specific against lysozyme (LS) was bound to Sepharose 4 Fast Flow gel to propare anti-LS Ig Y-immunoaffinity chromatographic column, to which diluted hen egg white and duck egg white were applied to determine and compare the changes in specific activity, recovery (%), and purification efficiency. It was observed that specific activity of isolated LS from hen egg white was about 44830 units/mg protein with a recovery of 94%, whereas that of isolated duck egg white was about 15460 units/mg protein with a recovery of only 12%. By repeated application of various amounts (0-5.75 mg LS/mL) of LS in commercial LS product or diluted hen egg white to anti-LS Ig Y-Sepharose 4 Fast Flow immunoaffinity chromatography, it was found that the binding capacity (qm) of this anti-LS Ig Y-immunoaffinity gel for commercial LS was 0.16 mg/mL wet gel, higher than that (0.11 mg/mL wet gel) of the immunoaffinity gel for diluted hen white. In contrast, the dissociation constant (Kd) of suck immunoaffinity gel for LS in diluted hen egg white was 3.72�10-8 M for commercial LS. It suggests a relatively weaker immunoaffinity between diluted hen egg white LS and anti-LS Ig Y-immunoaffinity gel.