Three kinds of imidazolium ionic liquids were synthesized, and [Bmim][CH3COO] was selected as a result of its higher deacidification rate at a lower cost. Then, the synthetic ionic liquid was immobilized by layered double hydroxides, and the composites were characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance (13C NMR), electrospray ionization mass spectrometry (ESI–MS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and N2 adsorption–desorption isotherms. The results showed that [Bmim][CH3COO] synthesized by the intercalation method exhibited a better deacidification property compared to the dipping method. When [Bmim][CH3COO]/Mg0.5Ca2.5Al1 (I) synthesized by the intercalation method was used as a reagent, the deacidification rate reached 97.61%. The optimum reaction conditions were at the reagent/oil mass ratio of 0.08, the reaction temperature of 313 K, and the reaction time of 1 h. Moreover, the composites still had excellent performance on deacidification after being repeatedly used 6 times.