PURPOSE: To obtain the subject catalyst having high immobilization ratio and capable of miniaturizing a reactor by adding a phosphoric acid esterified pulp to a biological catalyst suspension to form a hydroged, dispersing the hydrogel into a sodium alginate solution and gelling the dispersion with CaCl2.

CONSTITUTION: A highly water-absorbable material such as phosphoric acid esterifiel pulp prepared from sterilized chlorite-treated Abies sachalinensis powder, etc., is added to the lyophilized matter of the suspension of lactobacillus, etc., previously cultured to form a hydrogel containing a biological catalyst such as lactobacillus. The hydrogel is added to sterilized 3% sodium alginate aqueous solution and the mixture is stirred until the hydrogel is formed into fine particles uniformly dispersed, and the resultant solution is dropped to sterilized 2% calcium chloride aqueous solution so as to gel the solution to provide the objective immobilized biological catalyst in which hydrogel of highly water- absorbing material containing the biological catalyst is included and immobilized, which is excellent in immobilization yield of the biological catalyst and has high ratio of biological catalyst immobilized per unit volume and can miniaturize a reactor.