To provide a method for preparing a super high-density antimicrobial basic material which is useful for improving the soil environment, has enhanced antagonistic activity against a soil microorganism phase and comprises high- density actinomycetes, bacteria, filamentous fungi and yeast.

This method for preparing a super high-density antimicrobial basic material comprises a stage in which an organic medium comprising rice bran as a main raw material is inoculated with a soil microorganism mixture of actinomycetes of the genus Streptomyces, bacteria of the genus Corynebacterium, filamentous fungi of the genus Aspergillus and yeast of the genus Saccharomyces as main components and a crude microorganism is obtained by subculture and a stage in which the obtained crude microorganism is inoculated into a culture medium composed of ground soil of mineral of volcanic rocks, a formulated nutriment and water, the culture product is cultured for a fixed time and properly stirring and aeration are carried out in accordance with rise in temperature.