The current study investigates the behavior of strength and expansive characteristics of black cotton (BC) soil by applying nano-chemicals and commonly available industrial waste product fly ash. A sequence of laboratory tests through the utilization of unconfined compressive strength (UCS), California bearing ratio (CBR), and free swell index (FSI) has been performed by using organosilane chemicals (terrasil and zycobond) and fly ash admixed with different proportions from 0.03–0.1% and 0–20% of the dry weight of BC soil. Finally, the optimum dosage of nano-chemical and fly ash-treated soil samples was mixed to assess the combining effect of both additives. The experimental results specify that the incorporation of nano-chemicals and fly ash into black cotton soil results in a substantial improvement in the strength and swell behavior of the soil. However, the improvement trend follows up to a specific dosage, i.e., 0.08% of nano-chemical and 10% of fly ash; beyond that, the percentage increase in improvement does not influence much. The present study provides a summary of the application of nano-chemicals and fly ash as stabilizing agents to enhance the expansive soil’s characteristics.