PURPOSE: To obtain myo-inositol dehydrogenase having excellent heat-stability, etc., and exhibiting specific substrate specificity, enzymatic action, etc., at a low cost by culturing a microbial strain belonging to genus Bacillus and capable of producing myo-inositol dehydrogenase in a medium and separating the subject enzyme from the cultured product.

CONSTITUTION: A microbial strain belonging to genus Bacillus and capable of producing myo-inositol dehydrogenase (e.g. Bacillus sp. No.3, FERM BP-3013) is cultured in a medium and myo-inositol dehydrogenase is separated from the cultured product. The enzyme has substrate specificity to myo-inositol and catalyzes the reaction to produce myo-inosose, NADH and H+ from myo-inositol and NAD+. The residual activity of the enzyme is ≥95% at 60°C and a reagent for determining myo-inositol in high accuracy can be produced by using the enzyme.