PURPOSE: To easily obtain a microorganism-immobilized carrier having high activity by immobilizing microorganisms to β-chitin.

CONSTITUTION: A microorganism-immobilized carrier having excellent substrate permeability and strength can be produced by immobilizing a microorganism to β-chitin obtained e.g. from cuttlebone. It can be produced by suspending thoroughly crushed β-chitin in water at a concentration of about 5-20wt.%, dispersing the formed gel in water, adding a suspension of microbial cells and drying and forming the mixture.