Expansive soils (ES) are prevalent in semi-arid regions, notably in North African countries. Such soils pose significant infrastructure challenges due to their shrink-swell behavior upon moisture variation. Stabilizing ES using tailings offers a dual benefit: enhancing soil properties and addressing tailing disposal concerns. Reusing and recycling mine tailing materials in problematic earthwork applications, such as ES, could mitigate environmental pollution due to mining activities and protect natural resources. This work is the first study to demonstrate the pozzolanic reactivity and mechanical benefits of finely ground Algerian iron ore tailing (IOT) as a standalone stabilizing agent for ES. Soil samples were treated with varying IOT concentrations (8%, 10%, and 12%) and subjected to a series of tests, including sieve analysis, X-ray fluorescence (XRF), scanning electron microscope (SEM), and X-ray diffraction (XRD). Geotechnical properties were assessed through standard Proctor compaction, unconfined compression strength (UCS), free swell, oedometer, and shear strength tests over different curing periods. Results show that the IOT effectively reduces ES expansion and improves the properties by decreasing plasticity index (PI), free swell index (FSI), swelling pressure (Sp), and maximum dry density (MDD), as well as increasing optimum moisture content (OMC), cohesion (C), frictional angle (phi) and pH. The mixture with 12% IOT demonstrated the highest improvement in compressive strength, highlighting its efficiency in stabilizing ES. This research proves the ability of IOT as a sustainable stabilizer for ES. It gives a second use to tailing material in geotechnical projects.