<p>Radioactive barium discharge into the environment is a big problem due to its toxicity and mobility. This paper describes the characterization of sulphonated polystyrene pellets (SPSP) using Fourier transform infrared (FTIR) and energy-dispersive X-ray spectroscopy (EDX). Batch studies were conducted to study the sorption of Ba(II) onto sulphonated polystyrene pellets (SPSP), and the adsorption efficiency (S%) was found to be 96% at pH 4.0 and contact period of 120 min. Experimental thermodynamic studies support the exothermic character of the SPSP/Ba system and the negative value of ∆S, indicating a non-random interaction of Ba(II) on the surface of SPSP during the adsorption process. Nonlinear isotherm models such as Langmuir, Freundlich, and Temkin were used to fit the equilibrium data. The kinetic data were fitted using nonlinear kinetic models such as pseudo first order, pseudo second order, intraparticle diffusion and Elovich. The adsorption process of Ba(II) onto SPSP was fitted to the pseudo first order kinetic model and with the Langmuir adsorption isotherm model, with a maximum adsorption capacity of 12.79 mg/g. Nonlinear isotherm and kinetic models results were interpreted using the coefficient of determination (R²), Marquardt's percent standard deviation (MPSD), Hybrid fractional error function (HYBRID), Sum of absolute error (EABS), Sum square error (SSE) and Average relative error (ARE) functions for error calculation and goodness of fit. This study demonstrates the effectiveness of sulfonated polystyrene pellets (SPSP) as an efficient and low-cost adsorbent for barium uptake from contaminated wastewater.</p>