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Heavy metal pollution poses an environmental risk, and its efficient removal and facile separation from water remains a challenge. Magnetic iron oxide, an eco-friendly, relatively stable, and easy-separation material, has been regarded as one of the most applicable adsorbents for water treatment. However, the limited adsorption capacity has restricted its applications. Herein, sulfur-doped magnetic Fe₃O₄ (S_x–Fe₃O₄) adsorbent was fabricated using a calcination method for the efficient removal of Pb(II) from water. In contrast to undoped Fe₃O₄, the introduction of doped sulfur greatly enhanced the adsorption performance of S–Fe₃O₄ over four times, with a maximum capacity of 333.33 mg g⁻¹, which was synthesized at 300 °C with a raw molar ratio of S–Fe of 5. Based on the structure and morphology analysis, it was demonstrated that sulfur was successfully doped into the Fe₃O₄ structures, which resulted in Fe₃O₄ with active sulfur sites accordingly contributing to the adsorption enhancement through the combination of strong soft–soft interactions between soft base sulfur and soft acid Pb(II) along with surface adsorption. S_x–Fe₃O₄ could maintain the adsorption performance in the presence of competing ions. Furthermore, although the sulfur doping process exhibited slight side effects on the magnetic property, magnetic S_x–Fe₃O₄ maintained the high separation potential. This study presented a promising strategy to enhance the adsorption performance of Fe₃O₄ through sulfur doping for Pb(II) removal from water.