Abstract: : Nearly 51.8 million hectares of land area in India are covered with Expansive soil. The property of expansive soil is hard in dry state soft in wet state because of cohesiveness. Due to cohesiveness property in expansive soil it became weak and good for foundation or pavement subgrade. Soil Stabilization is one of the most important aspects for construction industry, which is used widely in foundation and road pavement constructions; this is because such stabilization improves geotechnical properties of the soil, such as volume stability, strength and durability. The process of removing weaker soil or adding the binder materials to soil to make the stabilization. In the present study, using fly ash to stabilize the black cotton soil obtained from site. With various proportions of i.e. 10%, 20%, 30%, 40% & 50%, expansive soils are stabilized. In conclusion, addition of fly ash results in decrease in plasticity of the expansive soil, and increase in workability by changing its grain size and colloidal reaction.