Abstract: The adsorption and desorption behaviors of S-metolachlor in three different soils were investigated using the batch equilibration method.The results showed that the adsorption isotherms (L-type) fitted the Freundlich equation well,and the adsorption constant (Kf) of S-metolachlor were 4.01,6.15 and 8.62.Based on the correlation between Kf (1/n) (n is empirical constant) and organic matter content of soils,it was concluded that organic matter content was a dependent factor in the soil adsorption.S-metolachlor desorption isotherms showed hysteresis,which did not coincide with adsorption isotherms.Furthermore,the adsorption concentration of S-metolachlor in soils was reduced at high temperatures,and the adsorption concentration was relative low at neutral condition.