Abstract Transition metal catalysis has played an important role in modern organic chemistry. In order to develop highly efficient and sustainable methodologies, considerable efforts have been devoted to combining the benefits of homogeneous catalysis and heterogeneous catalysis. Porous organic cages (POCs) are a relatively new type of discrete molecules with permanent cavities and good solubilities. These intrinsic properties make POCs expedient catalyst support for the homogenization of heterogeneous transition metal nanoparticles (MNPs). This review mainly focuses on the recent progress of MNPs‐catalyzed reductions and coupling reactions within POCs. In most cases, the MNPs@POC complexes have exhibited outstanding reactivity, dispersibility, stability, and reusability. These pioneering contributions have enriched the methodology toolbox for advanced organic synthesis.