To decontaminate a contaminated soil to prevent the generation of new environmental damage due to the disturbance of biosystem by bringing a crushed material of a decomposition microorganism structurally providing oxygenase and capable of decomposing the organic materials without a derived material into contact with the soil contaminated with an organic material.

The crushed material of the decomposition microorganisms structurally providing oxygenase and capable of decomposing the organic material without the derived material is brought into contact with the soil contaminated with the organic material to be decontaminated. In such a case, the organic material is limited to an aromatic compound or a chlorinated aliphatic hydrocarbon. And the chlorinated aliphatic hydrocarbon is limited to at least one of trichlorethylene and dichloroethylene. The decomposition microorganism is JM 1 (FERM BP-5352), JM 2N (FERM P-15691), JM 6U (FERM P-15692), JM 7 (FERM P-15718).