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The adsorption and movement of cypermethrin in different types of uncontaminated soils in acetone-water mixtures at different f s values has been studied by batch shake and soil thin-layer chromatographic techniques, respectively. Higher adsorption and a reduced movement of cypermethrin was observed on silt clay loam soil followed by loam and sandy loam soils and was anticipated by the Freundlich adsorption constants K m and R f values. The K m and R f values also confirmed that the adsorption of cypermethrin decreased while its movement increased with increasing f s values. The values of the Freundlich constant K m were used to evaluate the cosolvent theory for describing the adsorption of cypermethrin in acetone–water mixtures. For each soil, the values of the adsorption coefficient K m decreased in a linear logarithmic fashion as f s increased, the slopes of the log K m versus f s plots being essentially the same for all soils. Thus, the cosolvent effects on adsorption could be expressed by a single parameter (σ s ) which combines the characteristics of the solvent (acetone) and the adsorbate (cypermethrin). For adsorbates with a low solubility in aqueous solutions, the adsorption data from mixed solvents was extrapolated to f s = 0 to estimate the values of the adsorption constant K w in the aqueous phase.