The increasing threat of chloride ions (Cl⁻) has led researchers to explore efficient removal technologies. Sewage treatment with a double-layer hydroxide/oxide (LDH/LDO) is receiving increasing attention. In this work, Mg-Al LDO adsorbents were produced by the calcination of the Mg-Al LDH precursor, which was constituted by improved coprecipitation. The influence of calcination temperature, calcination time, adsorbent dosage, Cl⁻ initial concentration, contact time, and adsorption temperature on Cl⁻ elimination was investigated systematically. The experimental results showed that a better porous structure endowed the Mg-Al LDO with outstanding adsorption properties for Cl⁻. The adsorption process was well matched to the pseudo-second-order kinetics model and the Freundlich model. Under optimal conditions, more than 97% of the Cl⁻ could be eliminated. Moreover, the removal efficiency was greater than 90% even after 11 adsorption–desorption cycles. It was found that the electrostatic interaction between Cl⁻ and the positively charged Mg-Al LDO laminate, coupled with the reconstruction of the layer structure, was what dominated the Cl⁻ removal process.