Numerous Studies have shown that freeze-dried smectite clays have a high affinity for organic contaminants and pesticides from water. Research has shown that the surface charge density and exchangeable cations play a dominant role in controlling the sorption of organic pollutants by smectites, but there is a paucity of studies quantifying the interactions between organic contaminants and pesticides with smectites under environmentally relevant conditions. This study was undertaken to determine the effect of clay hydration on the sorption of 1,3-dimethylisophthalate (DMI) by a reference Wyoming smectite saturated with K⁺ and Ca²⁺. The results indicate that K⁺-saturated never-dried clay had higher DMI sorption than K⁺-saturated freeze-dried clay, while the opposite was true for Ca²⁺-saturated smectite. K-saturated clay sorbed more DMI than Ca-saturated clay. This can be attributed to the lower hydration energy and hence smaller hydrated radius of K⁺, which maximizes the siloxane surface available for sorption. The relatively weak hydration of K⁺ causes K-saturated clay to swell less in water, thus providing a more favorable sorption domain that may allow the organic substances to compete better with water for coordination sites around the cations. Increased loading of DMI resulted in significant increase in DMI sorption by freeze-dried clay only.