【Objective】Soil colloid stability plays an important role in soil nutrient retention, structure formation and crop growth. The application of organic materials is an effective method for improving saline-alkali soil, but their effects on soil colloid stability in these conditions remain unclear.【Method】In this study, we investigated the effects of biochar (BC), cattle manure (CM), and maize straw (MS) on soil colloid stability at different salinity-alkalinity levels (non-saline-alkali, mild saline-alkali and moderate saline-alkali) through soil incubation and sedimentation experiments in the laboratory.【Result】(1) The addition of organic materials significantly reduced the diameter of saline-alkali soil colloidal particles, making it similar to the diameter of non-saline-alkali soil colloid. In mild saline-alkali soil, the effect of MS treatment was most effective, and the colloidal particles size decreased from 785.7 nm to 360.2 nm. In moderate saline-alkali soil, the effect of CM treatment was most effective, decreasing the colloidal particles size from 675.8 nm to 393.6 nm. (2) The stability of soil colloid is related to the degree of soil salinity. Compared with non-saline-alkali soil and mild saline-alkali soil, moderate saline-alkali soil colloid exhibited significantly high stability, likely due to elevated high pH and high alkalinity. (3) Organic materials had minimal effect on the colloid stability of non-saline-alkali soil and mild saline-alkali soil. However, CM and MS treatments significantly reduced the colloid stability of moderate saline-alkali soil, causing colloidal particles agglomerated. Therefore, in moderate saline-alkali soil, the application of cow manure and maize straw may be more effective than biochar for stability improvement.【Conclusion】The application of organic materials ameliorates the basic physicochemical properties of saline-alkali soil and optimizes the state of soil colloid. Compared with biochar, cattle manure and maize straw, due to their rich functional groups and nutrients, significantly reduced the colloid stability of moderate saline-alkali soil upon application, thereby inducing colloidal aggregation and promoting the formation of microaggregates.