This study investigates the mechanical behavior of clayey soil treated with terrazyme, focusing on its impact on soil characteristics. Various dosages of terrazyme were used to study the effect on its geotechnical properties, including Atterberg limits, plasticity index, optimum moisture content, maximum dry density, unconfined compressive strength (UCS), California bearing ratio (CBR), Toxicity Characteristic Leaching Procedure (TCLP) and microstructure. The addition of terrazyme led to an increase in MDD from 19.71 kN/m³ to 24.02 kN/m³ at a dosage of 1.6, while OMC decreased from 13.45% to 9.45%. Terrazyme treatment decreased the Plasticity Index (PI) from 23% to 8%, raised the Plastic Limit (PL) from 29% to 32%, and decreased the Liquid Limit (LL) from 52% to 40%. At a dosage of 1.7, UCS rose from 150 kPa to 156.2 kPa, and after 28 days, it increased even more to 300.5 kPa. As a result of improved soil microstructure, CBR values increased from 3% to 14% after 7 days and from 5% to 25% after 28 days. Terrazyme proved highly effective in reducing Hg, Ba, and Pb concentrations to within EPA limits, with the 1.8 concentration yielding optimal results. Scanning Electron Microscope (SEM) analysis revealed a denser particle packing in the treated samples. The research highlights the need for a comprehensive and systematic investigation into enzyme-based soil stabilization, emphasizing the importance of understanding soil-enzyme interactions for practical geotechnical applications.