Strain UK 788 (FERM-P No. 5141) that belongs to Bacillus stearothermophilus, the cell of which is longer than about 10 microns and which permits easier release of intracellular components than a type culture Bacillus stearothermophilus, IAM 11001 is disclosed. Also, a process for producing a useful enzyme selected from the group consisting of a heat-resistant polynucleotide phosphorylase, heat-resistant maleate dehydrogenase, heat-resistant glucokinase, heat-resistant glucose-6-phosphate dehydrogenase and heat-resistant pyruvate kinase by culturing such UK 788 and recovering the desired enzyme from the culture is disclosed. Since the cell of the strain UK 788 is easy to settle and its membrane is also easy to break, the useful enzymes mentioned above can be efficiently produced on an industrial scale.