The polymer inclusion membrane (PIM) containing tri-n-butyl phosphate (TBP) and ferric trichloride (FeCl3) is capable of separating Li+ and Mg2+. However, many problems remain to be resolved, such as the need of a high concentration of Cl− in the stripping phase, low stability due to loss of Fe3+, and complex preparation process of the carrier used for PIM. In order to solve these problems, hydroxyl-functionalized ionic liquid 1-hydroxyethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([OHEMIM][NTf2]) instead of FeCl3 was incorporated into polyvinyl chloride (PVC)-based PIM in this study. PIM was characterized by Fourier transform infrared spectroscopy, scanning election microscopy, and thermogravimetric analysis, and the effects of the pH of the initial aqueous phase and the mass ratio and concentration of carriers on the extraction efficiency were investigated. Under optimum conditions, the extraction efficiency of Li+ and the separation factor of Li+ over Mg2+ are increased by 13.3% and 24.8% compared to liquid–liquid extraction, respectively. After 10 cycles, the extraction efficiency of Li+ is slightly decreased from 17.0 to 13.6%, indicating that PIM is relatively stable. In the transport experiment, the initial flux of Li+ is 1.6 × 10–3 mol·m−2·h−1 and the separation factor of Li+ over Mg2+ is 184 under optimum conditions, which demonstrates that Li+ can be effectively and selectively separated from Mg2+. It is also found that a high Cl− concentration is not needed in the stripping phase. This study can facilitate the application of PIM for extraction of Li+ from brine with a high Mg/Li ratio.Graphical Abstract: