waste has been modified by sulfonation using sulfuric acid to form its corresponding sulfonated adsorbent and was further used for removing cadmium ion in its aqueous solution. The effect of the styrofoam weight, sulfuric acid concentration, temperature and time on the sulfonation result was evaluated. The prepared adsorbent was characterized by XRD, FTIR, and SEM. The cadmium ion adsorption was conducted by batch technique, where the kinetic parameters were determined. The research results attribute that the sulfonated styrofoam has been successfully prepared, and the highest sulfonation is exhibited by using 18M of the sulfuric acid, at 60 oC for 6 h with 5 g of styrofoam. The cadmium adsorption by the sulfonated styrofoam fits with the pseudo-second-order and the Langmuir isotherm model, while the native styrofoam follows the intraparticle diffusion mechanism and Freundlich isotherm model. The adsorption capacities of the sulfonated and the native styrofoam are 51.6 mg/g and 7.09 mg/g respectively, and their respective adsorption rate are 8.20 10-3 mg. g-1. min-1 and 26.9 10-3 mg.g-1 min-1/2 .