Herein, a series of carbocatalysts containing Ru-based clusters have been prepared by the assistance of zeolite-imidazolate frameworks (ZIFs). The introduction of Ru is based on the adsorption of well-defined Ru3(CO)12 within the cavity of ZIFs following decomposition at 900 °C. Moreover, without breaking the skeleton and porosity of ZIFs, the as-generated Ru species would bond with the Co nodes in situ to form bimetallic Ru-Co clusters if the Co-bearing metal-organic frameworks were utilized as the host. Within the confined space of ZIFs, the assembly of Ru and Co could be rationally designed, and their structures could be sophisticatedly controlled at the atomic scale. Among these Ru-based compositions, the Ru-Co clusters@N-C exhibited remarkable catalytic activity for the NH3 decomposition to H2 and NH3 synthesis versus Ru-Co NPs@N-C, Ru clusters@N-C, and Ru NPs@N-C. This study may open up a new routine to synthesize metallic clusters or other subnano structures by the confinement of ZIFs.