<p>A magnetic adsorbent was prepared by combining ionic liquid with polyhedral oligomeric silsesquioxanes (POSS)-modified composite. In brief, POSS and ionic liquids were sequentially grafted onto magnetic silica nanoparticles via the radical polymerization reaction. Several analytical methods were employed to characterize the synthesized adsorbent. By introducing the branched polyhedral oligomeric silsesquioxanes, the fabricated magnetic adsorbent possessed a high density of multiple active sites, such as charged imidazole groups, alkyl chains, and benzene rings, and showed excellent adsorption efficiency for Allura Red. The effects of adsorbent type, pH, adsorbent dosage, and eluent were studied. In addition, the magnetic adsorbent could be reused even after 6 adsorption–desorption cycles with an 82% removal efficiency, implying good reusability. The composite showed excellent removal efficiency for Allura Red (93.6%) in sewage, with a maximum adsorption capacity of 309.6 mg/g. The adsorption of Allura Red was fitted by the Langmuir model, implying a uniform distribution of adsorption sites within a binding layer. The adsorption mechanism was also discussed, and electrostatic interactions may be mainly responsible for Allura Red adsorption. All the results indicated that the prepared adsorbent can be used for the removal of anionic dyes from sewage effectively.</p>