Alpha-D-Xylosidase II activity from Aspergillus flavus MO-5 was increased roughly 5- to 10-fold by use of xylose instead of methyl alpha-D-xylopyranoside (alpha-MX) as a carbon source. The enzyme was purified to an electrophoretically pure state by successive chromatography on Q-Sepharose, Phenyl Superose, PL-SAX, and TSK-gel G3000SWXL. The purified enzyme hydrolyzed isoprimeverose [alpha-D-xylopyranosyl-(1-->6)-D-glucopyranose] and p-nitrophenyl alpha-D-xylopyranoside (alpha-p-NPX), but not alpha-MX or xyloglucan oligosaccharide. The apparent Km and Vmax of the enzyme for alpha-p-NPX and isoprimeverose were 0.97 mM and 28.0 mumol/min/mg protein, and 47.62 mM and 2.0 mumol/min/mg protein, respectively. This enzyme had an apparent molecular weight of 67,000 by SDS-polyacrylamide gel electrophoresis and 180,000 by gel filtration chromatography (TSK-gel G3000SWXL). The enzyme showed the highest activity at pH 6.0 and 40 degrees C, and was stable in the pH range from 6.0 to 7.0 and at the temperatures up to 40 degrees C. The activity was inhibited by Cu2+, Zn2+, Hg2+, p-CMB, SDS, Fe3+, and N-ethylmaleimide. This enzyme had nothing in common with alpha-D-xylosidase I and four alpha-D-xylosidases reported already.