Due to the existing challenges in the synthesis of covalently linked large organic cages, the potential benefits of such gigantic structures have been less explored, comparatively. Here, we present a one-pot, template-free strategy to construct a porphyrin-based gigantic organic cage P12L24, built with 12 square-shaped porphyrins (P) and 24 bent linkers (L). Single crystal X-ray analysis of P12L24 revealed a cuboctahedron structure with a diameter of similar to 5.3 nm reminiscent of the COPII protein with a cuboctahedral geometry. To the best of our knowledge, it represents the largest, pure organic synthetic cage reported so far. By virtue of its large voids facilitating mass transport of substrates, 3a efficiently catalyzes the photooxidation of dihydroxynaphthalene derivatives in a heterogeneous setting, corroborating the benefits of these structures. Additionally, we demonstrate the insertion of a linear guest molecule into Zn-metallated cage Zn-3b in solution, which may facilitate the synthesis of multivariate gigantic cages in the future.