A useful microorganism (lactic acid bacteria) was immobilized in biodegradable microcapsule utilizing the solvent evaporation technique of water-in-oil-in-water (W/O/W) emulsions. We optimized the preparation conditions of the microcapsule immobilizing a useful microorganism through the experiments. As a result, the optimized microcapsule could efficiently immobilize the microorganism with a high activity. The lactic acid production activity of the microcapsules prepared under the optimized condition was approximately nine times higher than that of a commercial soil conditioner. Soil application demonstrated that the microcapsules are effective for the disinfestation of the root-knot nematode.