Polymerized ionic liquids (PILs) membranes demonstrated good potential for advanced separation potentials. To further improve the gas separation performance of PILs-based membranes, a flexible porous polypyrrolidinium membranes for CO 2 /N 2 separation has been developed through a one-step processing via a facile ring-openingmetathesis polymerization (ROMP), the resulting porous polypyrrolidinium membranes showed CO 2 permeability of 209 Barrer (PCPy-TFSI) and CO 2 /N 2 selectivity of 46.9 (PCPy-PF 6 ). More importantly, the porous polypyrrolidinium membranes showed improved anti-aging performance compared with PIM-1 membranes. This newly-developed ionic porous polymer membranes will bring new possibilities to new MMMs technology in the near future.