Surface agglutinin was extracted from soybean (Glycine max L.) seedling surface with distilled water by a 91-minute immersion. The agglutinin in the seedling was age-dependent and detected maximally in cotyledon of 3-day-old seedlings. The agglutinin can agglutinate human group A red cells and trypsin-treated rabbit erythrocytes but cannot agglutinate human group B and O red blood cells. The hemagglutinating activity was specifically inhibited by galactose and N-acetyl-D-galactosamine. The soybean surface agglutinin (SSA) was purified by ammonium sulfate precipitation and N-acetylgalactosamine affinity chromatography. The optimum temperature for hemagglutination activity by SSA was 30-40 degree C and the optimum pH was 8.0 Gel filtration and SDS-polyacrylamide gel electrophoresis showed that SSA contained approximately 28,000 Dalton polypeptide subunit that was quite similar to that of commercial soybean agglutinin (SBA) (MW equal 29,000 Dalton). Isoelectric focusing gel electrophoresis revealed the pI of SSA to be 7.0, but in the SBA, two bands of proteins which pI equal 6.8 and 6.65 were found. Although the biological properties of both purified SSA and commercial SBA were quite similar, they display slight difference in pH optima, pI and lactose specificity. The purified SSA also had fungistatic effect on some soybean pathogenicfungi.