The study aimed to reduce leaching of the hydrophobic herbicide norflurazon (4-chloro-5-methylamino-2-(alpha,alpha, alpha)-trifluoro-m-tolylpyridazin-3-(2H)-one) by adsorbing it on clays or organo-clays. The surface of the clay mineral montmorillonite was modified from hydrophilic to hydrophobic by preadsorbing it with organic cations, of which thioflavin-T (TFT) at a loading corresponding to (5)/(8) of the cation-exchange capacity of the clay mineral yielded the highest affinity of adsorption of norflurazon. Pillared clay (PC) used without organic cations exhibited enhanced affinity for norflurazon adsorption, much higher than that of montmorillonite or sepiolite. Fourier transform infrared (FTIR) results showed interactions between aromatic moieties of preadsorbed TFT and the herbicide. Stronger interaction of the herbicide with a clay mineral or organo-clay corresponded to its slower release. Formulations prepared on the basis of montmorillonite-TFT and PC were more effective in reducing herbicide leaching in soil columns in comparison to the commercial formulation, whereas the herbicidal efficiencies were comparable.