Abstract: The stability of expansive soil can be improved after its treatment with ionic stabilizer(ISS). Laboratory tests of direct shear, water ratio limit and free expansive rate are conducted, before and after the soil is meliorated, to analyze the ISS improvement effect on the expansive soils with different initial moisture contents. Results show that the expansibility of the soil has been eliminated. The shear strength is improved dramatically when the initial moisture content is at the range of 11% to 30%. However, little effects are revealed outside the boundaries. The ionic stabilizer is neither adsorbed by capillary suction when the soil is dried nor stuck to soil surface due to the penetration of the solution in saturated state can react with all the clay particles. Findings of the experiment are of great significance in determining the initial moisture content when site improvements on expansive soil with ISS.