Exodextranase from Aspergillus ustus was purified by chromatography and characterized by various conditions. The optimal pH of the purified dextranase was 6.5 and this enzyme was maximally activated at $40^{circ}C$. The enzyme was stable at the temperature below $50^{circ}C$. The enzyme was markedly inactivated by $Hg^{2+},;Cu^{2+},;KCN;and;Co^{2+},;but;Ba^{2+},;Fe^{2+},$ cysteine, EDTA, and ascorbic acid enhanced the activity of the enzyme. The main products from the hydrolysis of dextran incubated with the dextranase were glucose, isomaltotriose and oligosaccharide. When dextran was incubated with the mixture of pullulanase and ${alpha}-amylase$, it was hydrolyzed into glucose, isomaltose and oligosaccharide. Polysaccharides in the decade teeth powder were hydrolyzed by the dextranase into glucose, isomaltotriose and oligosaccharides. In the hydrolysis of the teeth powder with the mixture of dextranase, pullulanase and ${alpha}-amylase$, were proved to be similar to the dextran hydrolysates.