A method for preparing an immobilized microorganism-complex having controlling activity against plant pathogenic microorganisms which comprises adding an inorganic salt of a polyvalent metal to a liquid containing a microorganism antagonistic to plant pathogenic microorganisms, drying the resulting cells of the microorganism so as to obtain them in the form of a powder, mixing the powdered cells of the microorganism with particles of humic acid obtained by extraction from compost to obtain aggregates, incorporating the aggregates with an aqueous carrageenan solution, and then drying the resulting mixture.
