PURPOSE: To stabilize soil in a short time by a method in which an improving agent containing an organic substance capable of discharging cations is added to water-containing soil, e.g., soft ground, and dewatered by pressing.

CONSTITUTION: Water-containing soil, e.g., soft ground, etc., is mixed with waste slag or soil, and an improving agent containing an organic substance capable of discharging cations is added to the mixture. The soil mixture is dewatered by pressing. As the organic substance capable of discharging cations, water-soluble organic sulfonic acid, carboxylic acid, or phosphoric acid, etc., discharging barium ion, strontium ion, calcium ion, etc., may be cited. The freeing of water can thus be accelerated and soil can be stabilized in a short time.