The instability of clay soil as a road subgrade due to its high shrinkage properties, results in frequent road damage. Therefore, adequate soil improvement is required to improve soil performance in order to satisfy post-construction stabilization requirements. Soil improvement is one of the efforts made to overcome it, such as the soil stabilization method. In recent years there has been an increase in research related to the chemical soil stabilization to improve the physical and mechanical properties of soils. The addition of chemicals such as palm bunch ash, lime, fly ash, and cement to clay soil results in hydration and pozzolanic reactions. This process results in changes in the physical and mechanical properties of the soil. The degree of soil stabilization is influenced by the type of additive, additive content, length of treatment, and soil mineralogy. This study discusses the changes that can affect clay soil when chemical stabilization is carried out, based on information provided by the authors.