【Objective】Sugar-clay aggregates play important roles in the transformation of nutrient elements such as phosphorus in soils. However, few studies have paid attention to the initial formation of microaggregates and subsequent adsorption of phosphorus mediated by the molecular weight of sugar in the nanoscale.【Method】In this experiment, a model clay, laponite, and representative sugars including glucose and dextran with different molecular weights were selected to serves the research objects. The formation of aggregates mediated by sugars with different molecular weights was observed by Raman spectroscopy and atomic force microscopy (AFM), and then the differences in interactions of laponite and sugar with different molecular weights were measured by single molecular force spectroscopy (SMFS). Finally, the content of phosphorus adsorbed by microaggregates was compared via the measurement of sorption isotherms of phosphate by laponite or sugar-laponite complexes.【Result】The molecular weight of sugar was important for interaction with laponite and the size of sugar-clay microaggregates increased with molecular weight, suggesting stronger interactions of laponite with the sugars. Phosphate adsorption was increased for sugar-laponite microaggregates compared to laponite because of an increase in the content of hydroxyl and surface Zeta potential of microaggregates. Also, the amount of phosphate adsorbed was observed to decrease with an increase in the molecular weight of sugar due to the greater particle size of high-molecular-weight sugar-laponite microaggregates.【Conclusion】The results showed that sugars with high molecular weight promoted the formation of microaggregates but disfavored the adsorption of phosphorus by microaggregates. These nanoscale observations will provide a new method and theoretical basis for understanding the biogeochemical cycle of phosphorus involved in microaggregates in soils.