The thermophilic fungus Thermoascus aurantiacus 179-5 produced large quantities of a glucosidase which preferentially hydrolyzed maltose over starch. Enzyme production was high in submerged fermentation, with a maximal activity of 30 U/ml after 336 h of fermentation. In solid-state fermentation, the activity of the enzyme was 22 U/ml at 144 h in medium containing wheat bran and 5.8 U/ml at 48 h when cassava pulp was used as the culture medium. The enzyme was specific for maltose, very slowly hydrolyzed starch, dextrins (2-7G) and the synthetic substrate (${alpha}$-PNPG), and did not hydrolyze sucrose. These properties suggest that the enzyme is a type II ${alpha}$-glucosidase. The optimum temperature of the enzyme was $70^{circ}C$. In addition, the enzyme was highly thermostable (100% stability for 10 h at $60^{circ}C$ and a half-life of 15 min at $80^{circ}C$), and stable within a wide pH range.