In this study, adsorption of the anionic surfactant, sodium dodecylbenzenesulfonate (SDBS), onto the cationic polymer, polyethlyleneimine (PEI)-modified bentonite clay (PMB), was investigated. In order to prepare PMB, the bentonite suspension was mixed with PEI and the adsorption kinetic and adsorption capacities of the PMB suspensions were determined using SDBS as adsorbate. Fourier transform infrared spectroscopy (FTIR) was used in the characterization of PMB. The adsorption studies of PMB were carried out using batch adsorption methods. The equilibrium was achieved in 10 min. Adsorption data were applied with several kinetic (pseudo-first-order, pseudo-second-order, intra-particle, and Elovich) and isotherm (the Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Temkin) models. All the experimental data of SDBS on PMB were analyzed with error functions as correlation coefficient (R-2) and the normalized standard deviation Delta q (%). Results indicated that for the adsorption kinetics, the best fit was provided from the pseudo-second-order kinetic model with R-2 value of 0.9999. For the adsorption isotherms, the best fit was obtained Langmuir and Temkin isotherms with R-2 value of 0.9968 and 0.9865, respectively. High adsorption capacity (q(m)) as 443.1 mg.g(-1) was determined from the Langmuir isotherm.