The deactivation mechanism and the activity recovery approach of composite ionic liquid (CIL), a kind of acidic chloroaluminate ionic liquids (ILs) modified with CuCl for the in 2013 successfully commercialized catalysis of isobutane alkylation are being discussed in this paper. CIL showed catalytic activity only in the presence of both Bronsted and Lewis acids. CIL deactivation was caused by the loss of Bronsted acidity and/or Lewis acidity. Bronsted acidity decreased by the loss of trace amount of formed chlorohydrocarbons with the outflowing alkylate. Lewis acidity was deactivated mainly due to the complexation of the formed acid soluble oil (ASO) with the CIL anions. Bronsted acidity was maintained by the continuous addition of hydrogen chloride (HCl) or tert-butyl chloride, and Lewis activity was recovered by AlCl3 addition. However, Bronsted acidity could not be recovered when Lewis acidity was lost and was thus dependent on Lewis acidity. Furthermore, ASO interacted with active components of CIL, causing the loss of copper via precipitation of CuCl which is the major contributor to the high selectivity. Therefore, CuCl was added simultaneously with AlCl3 to maintain the high selectivity of alkylate.