We present a high-performance polymeric membrane based on self-cross-linkable poly(glycidyl methacrylate-g-poly-(propylene glycol))-co-poly(oxyethylene methacrylate) (PGP-POEM) graft copolymer for CO2/N2 separation. The self-cross-linked membranes can be easily prepared under mild conditions without any additional cross-linking agents or catalyst. We investigated the gas separation performance of the membranes as a function of POEM content in the copolymer. The self-cross-linked PGP-POEM membranes showed an improvement in both permeance and selectivity with increasing POEM content up to 51.2 wt %. The best performance of the membrane was achieved by optimizing membrane thickness, showing a CO2 permeance of 500 GPU (1 GPU = 10-6 cm3 (STP)/(s cm2 cmHg)) and CO2/N2 selectivity of 22.4.