Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons. Thus, such problematic soils should be completely avoided or properly treated when encountered as subgrade materials. In the present study, the biomedical waste incinerator ash (BWIA) and lime combination was proposed to stabilize expansive soil. Particle size analysis, Atterberg limits, free-swell, compaction, and California bearing ratio (CBR) tests were conducted on the natural soil and blended with 3%, 5%, 7%, 9%, and 11% BWIA. The free-swell index kept on decreasing up to 9% BWIA and it became a bit raised when the soil was blended with 11% BWIA, but the reduction is not that much significant. Since the expansiveness of the soil has not decreased tremendously, additional lime was amended and further investigations on the strength of the soil have been performed. In addition, scanning electron microscopy (SEM) tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding. The addition of BWIA has a promising effect on the strength of the expansive soil. The strength of the expansive soil significantly increased when it was blended with 9% of BWIA amended by 2% and 3% lime. The CBR of the raw expansive soil was 2.3%. When it was treated with 9% BWIA and 3% lime, its CBR was significantly increased to 11.2%. The SEM micrographs showed that the raw expansive soil was dispersed (non-flocculated) fine particles with an open structural arrangement, but it became a homogeneous and flocculated structure when it was treated with 9% BWIA and 3% lime