The feasibility to synthesize the ligand-protected atomically precise nanoclusters with various compositions in sub-nanometer range (≤2 nm) and the determination of their structures is an important step in long-pursuit of well-defined heterogeneous catalysis. Such types of precise catalysts provide an opportunity to understand the fundamentals of catalysis better in terms of: 1) activity and selectivity by metal-core and metal-ligand interface, 2) size-dependent activity, 3) reaction mechanism and 4) active-site identification and activation. It motivated us to develop the novel metal nanoclusters with precise structures as the new catalytic systems, which led to the several significant findings on above mentioned points. We consider that with this gained knowledge, the future research is expected to bring more exciting advancement in deep understanding of the reaction mechanism, specific-site identification and tailoring of catalytic active sites at atomic level.