A thermophilic bacterium (strain DG0303) producing a thermostable $alpha$-glucosidase was isolated from manure and identified as Bacillus sp. Strain DG0303 produced high level of $alpha$-glucosidase compared with other thermophilic Bacillus strains. The cellular protein patterns were also compared with other Bacillus strains by sodium dodecyl sulfatepolyacrylamide gel electrophoresis(SDS-PAGE). On the basis of 16S rDNA analysis the Bacillus sp. DG0303 was found to be a member of Bacillus rDNA group 5. The optimum temperature for growth was 65$circ$C and no growth was obtained at 40$circ$C or 75$circ$C. The optimum pH for growth was 5.5 to 8.5. $alpha$-glucosidase activity was produced during growth and most activity was detected in the culture supernatant. The $alpha$-glucosidase production was constitutive in the absence of carbohydrates. High level of enzyme activity was detected when the culture was grown on medium containing starch. Addition of glucose resulted in the repression of the $alpha$-glucosidase production. The optimum pH and tempoerature for enzyme activity were pH 5.0 and 65$circ$C, respectively. When analyzed by zymogram, the culture supernatant showed a single $alpha$-glucosidase band with a molecular weight of approximately 60,000.