The present study investigates the potential of Simarouba glauca seed shell powder as a cost-effective adsorbent for the removal of the cationic dyes Malachite green (MG), Methylene blue (MB) and Rhodamine B (RB) from aqueous solutions. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD), as well as by Brunauer–Emmett–Teller (BET) and elemental (CHNS) analyses. Batch mode adsorption studies were carried out varying the experimental conditions, such as initial dye concentration and contact time, adsorbent dose, pH and particle size, in order to assess the adsorbent capacity for the removal of cationic dyes from wastewater. The experimental data were analysed using the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms. The data fitted well the Langmuir model for the dyes studied. Kinetic data were analysed using the pseudo-first order, pseudo-second order, intraparticle diffusion and Boyd models. The experimental results showed that the pseudo-second order model fitted well.