Abstract: Metal clusters are the nanomaterials, being composed of several metal atoms, having the feature sizes between those of individual metal atoms and nanoparticles, possessing distinct geometrical and electronic structures, and performing nicer in catalytic reactions. However, due to their high surface energy, the uncovered metal clusters tend to aggregate and deactivate during the catalytic process. So, in recent years, organic molecular cages (OMCs) have received much attention as new porous materials. Research results show that the metal clusters encapsulated in the confined space of organic molecular cages can not only improve their size homogeneity but also stability. And, the porous skeleton with an open channel can make the encapsulated metal clusters still maintain high catalytic activity in oxidation, reduction, coupling, hydrogen production, and other reactions. In this paper, the synthesis strategy of metal clusters encapsulated in organic molecular cages and the applications of such composites in the field of catalysis were summarized and reviewed.