PURPOSE: To obtain an immobilized mold having water-insolubility, high shape retention, and strength, and extremely low release of enzyme, by dispersing a mold of microorganism into an aqueous solution of a water-soluble high polymer substance, etc. to give a molded article of a compound mold, crosslinking it with a crosslinking agent.

CONSTITUTION: A mold of microorganism having D-threonine aldolase and/or L-allothreonine aldolase activity, and a water-soluble high polymer containing a hydroxyl group, amino group, or aldehyde group at the side chanin are prepared. The mold of microorganism is dispersed into an aqueous solution of the high polymer substance and chitosan. An alkali is added to the dispersion, to form a compound mold. It is then molded into a granular state, and treated with a crosslinking agent. The immobilized mold prepared by this method has water-insolubility, high shape retention, and strength, is packed into a column, and a substrate solution is made to flow through it to carry out an enzymatic reaction continously.