The adsorption and desorption of the herbicide imazethapyr,(RS)-5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid,on various soils were studied.Adsorption isotherms conformed to Freundlich equation.The K_f values increased with increasing organic carbon content of the soils.On the other hand,the behavior of imazethapyr in the soil is strongly affected by pH and clay content.As pH decreased,imazethapyr was more strongly absorbed,reducing its mobility and plant availability.Desoiption isotherms also conformed to Freundlich equation,but K_des values were higher than those of adsorption and increased with increase in the concentration of initially adsorbed imazethapyr.Through preparing the homoionic Na⁺-, Ca²⁺-,Cu²⁺-,and Al³⁺-saturated clay self-carrier membrane and using FT-IR,we studied the interaction mechanism of imazethapyr with the clay mineral.The results of X-ray diffraction also revealed that imazethapyr can enter the inner layer of bentonites and fornl complexes with the interlayer canons.