Abstract: Microbial Induced Carbonate Precipitation (MICP) technology has been widely applied for stabilizing coarse-grained soils such as sand. However, its effectiveness in loess stabilization is constrained by the fine particle composition and low permeability characteristics. This study introduces an active magnesium oxide-microbial stabilization approach for loess treatment. Taking Yan'an Q₃ loess as the subject, triaxial consolidated undrained shear tests are performed on loess stabilized with active magnesium oxide-microbial stabilization technology. The effects of Magnesium Oxide Content (MOC) on mechanical properties, including stress-strain characteristics, volumetric behavior, and shear strength properties of the stabilized loess, are investigated. The results indicate that the deviatoric stress-axial strain curves of the treated loess exhibit strain-softening behavior accompanied by brittle failure, with specimens exhibiting initial compression followed by dilation. Specimens sharing identical MOC maintain comparable elastic moduli during the elastic deformation phase. Higher MOC leads to more pronounced reductions in residual strength compared to peak strength, and this effect is partially mitigated by increased confining pressure. Peak deviatoric stress increases with both MOC and confining pressure. An empirical formula for peak deviatoric stress, considering MOC and confining pressure, is developed. Both effective cohesion and internal friction angle increase with MOC, but the rate of increase diminishes once MOC exceeds 10%. This study lays the foundation for the engineering application of magnesium oxide-microbial stabilized loess technology.