[Objective] To reveal the physicochemical properties of soil aggregates at different particle sizes and their influence mechanisms on cadmium（Cd）speciation，this study investigates the distribution characteristics of aggregates in typical paddy soils and the effects of aggregates with different particle sizes on Cd environmental behavior. [Methods] Two types of Cd-contaminated paddy soils were selected，namely granitic sandy soil（developed from granite）and eel clayey soil（developed from shale and slate）. Soil aggregates were separated into four size fractions using the wet-sieving method： macroaggregates （2-8 mm） ， intermediate aggregates （0.25-2 mm） ， micro-aggregates（0.053-0.25 mm），and silt-clay particles（<0.053 mm）. The effects of removing organic matter and free iron oxides from aggregates of different sizes on Cd adsorption were analyzed. [Results] Both soils were dominated by macroaggregates. The eel clayey soil exhibited a more stable aggregate structure than the granitic sandy soil，with higher mean weight diameter（MWD）and geometric mean diameter（GMD）. The granitic sandy soil had a higher proportion of small particle size aggregates with a looser structure and lower stability，mainly due to the lower mass fractions of organic matter and free iron oxides in its parent material. As aggregate size decreased，the organic matter，free iron oxide，and cation exchange capacity（CEC）of aggregates significantly increased. The adsorption capacity of all aggregates for exogenous Cd was enhanced with decreasing aggregate size，with the silt-clay particles demonstrating the strongest adsorption capacity. After the removal of organic matter，the Cd adsorption capacity significantly decreased，while the decrease after the removal of free iron oxides was relatively small. [Conclusion] The differences in aggregate composition and structural stability caused by different soil types significantly influence their Cd adsorption and speciation. These findings provide a scientific basis for understanding the evolution of heavy metal pollution in paddy fields and formulating remediation strategies.