AbstractThermostable α‐amylases produced by three different strains ofBacillusspecies are reported. The organisms are isolated from soil. They are designated asBacillus stearothermophilusA004,B. stearothermophilusAN002 andB. coagulansR3.The heat stable amylases produced by these organisms were partially purified and characterized. The temperature optimum forB. stearothermophilusA004 andB. stearothermophilusAN002 amylase is 80 °C, whereas the optimum temperature for amylase activity is 85 °C forB. coagulansR3.The amylases from all three strains show extremely broad pH ranges of activity (6.0–12.0). Furthermore, the α‐amylases fromB. coagulansR3retains 35% activity even at 0.1 n alkali solution. Action of these enzymes on starch produces glucose, maltose, maltotriose, maltotetrose and other higher oligosaccharides, indicating the α‐amylase nature of the t