The SDG-beta-D-glucosidase that hydrolyzes the glucopyranoside bond of secoisolariciresinol diglucoside (SDG) to release secoisolariciresinol (SECO) was isolated from Aspergillus oryzae 39 strain and the enzyme was purified and characterized. The enzyme was purified to one spot in SDS polyacrylamide gel electrophoresis, and its molecular weight was about 64.9 kDa. The optimum temperature of the SDG-beta-D-glucosidase was 40 degrees C, and the optimum pH was 5.0. The SDG-beta-D-glucosidase was stable at less than 65 degrees C, and pH 4.0-6.0. Ca(2+), K(+), Mg(2+) and Na(+) ions have no significant effect on enzyme activity, Zn(2+) and Cu(2+) ions have weakly effect on enzyme activity, but Fe(3+) ion inhibits enzyme activity strongly. The K. value of SDG-beta-D-glucosidase was 0.14 mM for SDG. (C) 2009 Published by Elsevier Ltd.