This research studies the potential of using bagasse ash to partially replace Portland cement Type I in ground improvement. The strength characteristic of cement-bagasse ash admixed Bangkok clay was investigated by means of a series of unconfined compression tests, paying special attention to the influence of ground bagasse ash in this mixture. From testing results, the unconfined compressive strength with an increasing of bagasse ash content. With the cement portions of equal to 20%, ground disposed bagasse ash could be employed as a pozzolanic material for partial replacement of cement in soft soil improvement. This will reduce the porosity of the soil cement due to the filling of the pores by bagasse ash. The results also demonstrate that the changes in the mineralogical contents and soil fabric of cement-bagasse ash treated soft clay improve soil plasticity, strength and compressibility.