The α-amylase (1, 4-α-d-glucanohydrolase; EC 3.2.1.1) and α-glucosidase (α-d-glucoside glucohydrolase; EC 3.2.1.20) secreted by Geobacillus thermodenitrificans HRO10 were purified to homogeneity (13.6-fold; 11.5% yield and 25.4-fold; 32.0% yield, respectively) through a series of steps. The molecular weight of α-amylase was 58kDa, as estimated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The α-amylase activity on potato starch was optimal at pH 5.5 and 80°C. In the presence of Ca 2+ , the α-amylase had residual activity of more than 92% after 1h of incubation at 70°C. The α-amylase did not lose any activity in the presence of phytate (a selective α-amylase inhibitor) at concentrations as high as 10mM, rather it retained 90% maximal activity after 1h of incubation at 70°C. EGTA and EDTA were strong inhibitory substances of the enzyme. The α-amylase hydrolyzed soluble starch at 80°C, with a K m of 3.05mgml −1 and a V max of 7.35Uml −1 . The molecular weight of α-glucosidase was approximately 45kDa, as determined by SDS-PAGE. The enzyme activity was optimal at pH 6.5–7.5 and 55°C. Phytate did not inhibit G. thermodenitrificans HRO10 α-glucosidase activity, whereas pCMB was a potent inhibitor of the enzyme. The α-glucosidase exhibited Michaelis–Menten kinetics with maltose at 55°C (K m : 17mM; V max : 23μmolmin −1 mg −1 ). Thin-layer chromatography studies with G. thermodenitrificans HRO10 α-amylase and α-glucosidase showed an excellent synergistic action and did not reveal any transglycosylation catalyzed reaction by the α-glucosidase.