Expansive soils pose significant challenges in construction due to their propensity for volumetric changes with varying moisture content. This study aims to compare the effectiveness of biochar and biomass ash as sustainable soil stabilizers for mitigating the expansive nature of soil. Laboratory experiments were conducted on expansive soil specimens incorporating varying percentages of biochar and biomass ash. The study assessed the impact of these stabilizers on the Atterberg limits, compaction characteristics, and unconfined compressive strength of the soil. Microstructural analysis was also performed to elucidate changes induced by the stabilizers. Preliminary results indicate that both biochar and biomass ash show promise in enhancing the engineering properties of expansive soil. The stabilizers led to improved strength characteristics, reduced swell potential, and alterations in soil microstructure. However, notable differences were observed in the extent of stabilization achieved by biochar and biomass ash. Further investigation is needed to optimize mixing ratios and assess long-term performance under various environmental conditions. This comparative study contributes valuable insights into sustainable soil stabilization method, offering a potential eco-friendly alternative to traditional stabilizers. The findings hold significance for geotechnical engineers and construction professionals seeking effective solutions for expansive soil-related challenges.