PURPOSE: To easily obtain α-1,3-glucanase useful for the decomposition of sordes on tooth, etc., on an industrial scale,by culturing a specific bacterial strain of Bacillus genus in a medium.

CONSTITUTION: Microorganisms capable of decomposing and utilizing insoluble glucan as a carbon source are identified to obtain Bacillus circulans BC-8 having a cell size of 0.5×1.3W2.6μm, exhibiting microbial properties such as Gram-positive bacillus and capable of producing α-1,3-glucanase which is an enzyme capable of specifically cutting and decomposting α-1,3-glucoside bond of 1,3-α-D- glucan existing in sordes on tooth, etc. The bacterial strain is cultured in a medium containing 0.1W/V% of insoluble glucan and peptone, etc., at 30W37°C and pH 6W7 for a desired period and the cultured liquid is subjected e.g. to centrifugal separation to recover α-1,3-glucanase having the following physical and chemical properties. Optimum pH, 4W9; optimum temperature, 45W50°C; inhibited by Hg2+, etc.; mol.wt., 180,000 (SDS-polyacrylamide gel electrophoresis); etc.