The sorption behaviors of nitrobenzene (NB) onto the soft K⁺ cation modified montmorillonite (K-Mt) under the conditions of adding of K⁺ ion and varying reaction temperatures were investigated in this paper. The sorption kinetic experiments showed that the sorption equilibrium of NB could be reached within 8 h. A comparative analysis of the Henry and Freundlich equations was made to evaluate the sorption isotherms of NB onto the K-Mt, and some thermodynamic experiments were conducted to explore the sorption mechanism. The results show that soft cation of K⁺ can strengthen the sorption of K-Mt for NB. The adsorption isotherms of NB by the K-Mt can be fitted well with Henry and Freundlich equation (R₂>0.96). Moreover, the research results of thermodynamic sorption experiments demonstrate that the sorption of NB onto the K-Mt is a spontaneous exothermic process mainly controlled by both the hydrophobic bonding and n-π electron-donor-acceptor (EDA) interaction between clay mineral surface and nitrobenzene. The presence of K⁺ ion is likely to be a favorable factor due to increasing some sorption sites and improving the accessing condition for sorption, leading to the promotion of sorption for NB onto the K-Mt.