PURPOSE: To efficiently obtain the subject preparation capable of sustaining the activity for a long period, having excellent long-term storage stability and useful for agriculture and horticulture by subjecting VA mycorrhizal fungi- containing soil to drying treatment under reduced pressure.

CONSTITUTION: Soil containing hypha, spore, etc., of VA mycorrhizal fungi is subjected to drying treatment under reduced pressure to provide the objective preparation. Furthermore, the preparation is preferably applied to soybean, Vicia sativa L., etc.