Abstract: Galactose-sepecific lectin from pseudomonas aeruginosa could agglutinate the erythrocytes of various animals (including rat, rabbit, mouse, sheep and pig) and the ability to agglutinate the erythrocytes treated with papain was stronger than those untreated except erythrocyte of chicken. The hemagglutination activity of lectin was inhibited by galactose, N-acetyl-galactosamine, lactose, raffinose, melibiose, xylosa and Na-EDTA, but not by glucose and N-acetylglu-cosamine. Binding of galactose to the lectin was assayed spectro-photometrically and the association constant for galactose was 6×10³L/ Mol. In addition, gel-filtration analysis revealed that the monomer of the lectin exhibited a tendency of aggregation.