The　high-yield　synthesis　of　ultrastable　porous　organic　cages　(POCs)　by　facile　methods　is　highly　desirable　but　challenging.　Inspired　by　highly　stable　sp2carbon-conjugated　(C=C)　covalent　organic　frameworks,　we　used　rational　design　and　synthesized　the　first　family　of　sp2carbon-linked　POCs　(sp2c-POCs)　with　triangular　prism　shapes　by　a　one-step　Knoevenagel　reaction　that　is　a　high　yield　[2+3]　condensation　reaction.　The　stability　of　sp2c-POC　was　demonstrated　under　strenuous　conditions　involving　for　example　concentrated　HCl　or　saturated　NaOH　solution.　sp2c-POC　was　used　as　a　robust　adsorbent　for　efficient　separation　of　CO2/CH4or　CO2/N2mixtures.　In　view　of　their　facile　synthesis　and　unique　properties,　we　expect　widespread　use　of　these　sp2C=C　linkages　in　the　development　of　POC　materials.　©　2023　The　Author(s).