The present disclosure concerns a soil or ground quality stabilizer comprising a mixture formed by mixing a burned sewage sludge ash the main contents of which are CaO, SiO.sub.2 and Al.sub.2 O.sub.3 with a lime of calcium hydroxide to reduce hydraulicity and a fine Fe oxides mixture powder byproduced in steel production the main content of which is iron oxide. The soil or ground quality stabilizer is added into a pavement material containing crushed stones, natural soil, etc. to improve the strength and viscoelasticity of the natural soil and can give a desired CBR strength to the soil having an increased moisture content. The preferable adding ratio of the fine Fe oxides mixture powder into the mixture of the burned sewage sludge ash and the lime of calcium hydroxide is within the range of 15-35 weight %.