Sepiolite was modified with polymer consisting of ethylenediamine(EDA)-trimesoyl chloride (TMC) to produce a highly effective sorbent for antimony (III) (Sb(III)) adsorption from aquatic solutions. The EDA-TMC polymeric branches were grafted onto the surface of sepiolite by polymerization. The surface morphology and the main adsorptive chemical groups of the developed S/EDA-TMC sorbent were characterized by SEM, EDX, BET, and FTIR, analysis methods. The impact of the batch adsorption conditions on the adsorption performance was systematically studied by conducting a factorial design analysis. While Langmuir and Freundlich isotherm models were employed with the non-linear equations to the removal data and the removal capacity of the prepared composite was estimated as 210.1 mg g−1 based on the Langmuir due to relatively high correlation. The kinetic investigation results displayed that the pseudo-second-order kinetic model was well appropriate for characterizing Sb(III) removal mechanism. Also, thermodynamic findings verified that the Sb(III) removal onto the composite adsorbent progressed exothermically and spontaneously with temperature increasing from 24° to 55°C. Besides, the produced adsorbent demonstrated still appreciated adsorption/desorption yield (80/76%) after the 7th cycle. Accordingly, the fabricated S/EDA-TMC material can be evaluated as a powerful sorbent in the cleaning of aqueous solutions containing Sb(III) pollutants. •Polymer modified magnetic sepiolite adsorbent was synthesized.•Sb(III) adsorption conditions were optimized with factorial design analysis.•Adsorption/recovery performance was considerable high at 7th cycle.