Abstract: The adsorption of the herbicide dimepiperate S-(α,α-dimethylbenzyl)-1-piperidinecarbothioate on homoionic Fe³⁺-, Al³⁺-, Ca²⁺-, and Na⁺-montmorillonite was studied in aqueous medium. The adsorption is described well by the Freundlich equation. The adsorption capacity decreases in the order Fe³⁺ > Al³⁺ > Ca²⁺ > Na⁺ clay. The dimepiperate adsorption from chloroform solution was also investigated by analytical, spectroscopic, and X-ray powder diffraction techniques. IR results suggest that the adsorption involves the interaction of the thioester carbonyl group of dimepiperate possibly with the surrounding water of metal ions. On Al³⁺ and Fe³⁺ clays, this interaction leads to hydrolysis of the thioester bond and formation of the thiol and carbamic acid derivatives that yield α-methylstyrene and piperidine, respectively.