Downstream separation and purification of monoclonal antibodies (mAbs) has long been the major bottleneck for their production. Here novel molecularly imprinted polymers (MIPs) of immunoglobulin G (IgG) were designed for their capture and separation from cell culture supernatant. To overcome the severe problems faced by protein-imprinted polymers, i.e., difficult template removal and low imprinting efficiency, a poly(L-glutamic acid) (PLGA)-based peptide crosslinker, instead of commonly used crosslinkers, was employed. In addition, a thiophilic functional monomer, 2-((2-hydroxy-3-(methacryloyloxy)propyl)thio)nicotinic acid (GMA-NA), which can bind with IgG selectively, was designed and used for the synthesis of IgG-imprinted polymers. Because of the reversible and precise pH-induced helix-coil transition of the PLGA segments in the polymers and also the selective binding of GMA-NA with IgG, complete removal of the template protein was achieved under mild conditions. Meanwhile excellent imprinting efficiency was obtained. For the IgG-imprinted polymer with an optimized composition, a high adsorption capacity (790.2 mg/g) and a high IF (5.2) were achieved, both of which are much higher than the previously reported IgG-imprinted polymers. The polymer exhibits high selectivity towards the template IgG against non-template proteins. It also exhibits excellent reusability. The high adsorption capacity, high selectivity and mild elution conditions of the new IgG-imprinted polymer make it good adsorbent for antibody separation. Using the new MIP, IgG was successfully separated from human serum. More importantly, HLA-DRA mAb was successfully separated from cell culture supernatant with a removal rate of 89% and a purity of 87%, confirming the potential of the new MIP in mAb separation.