【Objective】The aggregation and dispersion of soil colloids influence macroscopic phenomena such as soil structure, soil erosion, soil nutrients, and pollutant transport. This study aims to explore the process of purple soil colloid aggregation and its ion-specific effects under different fertilization treatments. Specifically, the study aims to elucidate the interactions and microscopic mechanisms from the perspective of the effect of fertilization on mineral composition, surface properties, and aggregation kinetics of purple soil colloids. 【Method】In this study, four fertilization treatments, no fertilizer (CK), urea alone (N), organic fertilizer replacing 10% urea nitrogen (LM), and organic fertilizer replacing 30% urea nitrogen (HM) were set up on a purple soil in Southwest China. After 60 d of incubation, the effect of fertilization on the colloid aggregation kinetics of purple soils and their causes were investigated by determining the colloid quantity, clay mineral composition and surface properties, and soil colloid aggregation process. 【Result】The colloids used in this study contained mainly hydromica, chlorite, montmorillonite, vermiculite, and kaolinite, and the short-term fertilization treatments had no significant effect on the colloid content and mineral composition. Compared to CK, the N treatment induced the highest surface charge density to the purple soil colloids, with the greatest electrostatic repulsion between particles whereas LM and HM treatments decreased the surface charge density, and the degree of decrease was directly proportional to the amount of organic fertilizer added. The aggregation kinetics of soil colloids differed under different fertilizations and the critical coagulation concentration (CCC) decreased in the order of N > CK > LM > HM. Under the same fertilization treatment, the CCC values of purple soil colloids showed an ion-specific effect, decreasing in the order of Na+, K+, Mg2+, and Ca2+. Also, correlation analysis showed that there was a strong positive correlation between the CCC values of purple soil colloids and the surface charge density and a strong negative correlation with the specific surface area and organic matter content. 【Conclusion】Different fertilization treatments affect the interaction force between soil particles mainly by influencing the surface chemical properties of purple soil colloids, thus, affecting the aggregation and dispersive behaviors of the colloids.