This study examines the influence of clay mineralogy, particularly clay content, Montmorillonite (MMT) %, on the swelling pressure of expansive soils. Through analyses of various soil samples collected from different sites, the research incorporates combination of physical properties tests, X-ray diffraction (XRD) analysis, microscope scanning (SEM), and swelling pressure evaluations, to establish the relationships. Results indicate that higher percentages of clay content, MMT and liquid limit consistently lead to increased swelling pressures. Clay mineralogy indicates the potential value of the swelling pressure, and although the quantitative values of the pressure are difficult to deduce from the data, it helps to explain the unusual behavior and identify the soil prone to swelling. Notably, The observed variability in swelling pressure among samples, even with similar mineral compositions, highlights the need for site-specific assessments. emphasize the critical importance of managing expansive soils to mitigate potential structural damage and optimize stabilization and construction practices.