Smectite clays have demonstrated high affinity for many organic contaminants and pesticides in aqueous solution, which is influenced by the intrinsic properties of smectite clays (e.g., surface charge density and location), exchangeable cations, and clay interlayer hydration status. The amount and the type of salts present in the aqueous phase determine clay quasicrystal structures, interlayer swelling property and hydration status, which we hypothesize as a major factor influencing sorption. To test this hypothesis, we measured sorption isotherms of 1,3-dinitrobenzene by K-smectite (SWy-2) in KCl solution and Ca-SWy-2 in CaCl2 solution at several ionic strengths. The results indicated that sorption by K-SWy-2 significantly increased with increasing aqueous KCl concentration. In contrast, sorption by Ca-SWy-2 at different ionic strengths of CaCl2 remained constant. The “salting-out” effect on the aqueous solubility of nitroaromatic compounds failed to account for the significantly increased sorption by K-SWy-2 with increasing KCl concentration. X-ray diffraction patterns indicated the formation of quasicrystal structures with a basal spacing at 15.5 angstrom in K-SWy-2 suspensions as KCl concentration > 0.1 M. We conclude that formation of better-ordered clay quasicrystals owing to increased KCl ionic strength facilitates the intercalation of nitroaromatic compounds leading to greater sorption by the clay, while the “salting-out” effect plays a minor role (if any) in observed enhanced sorption.