The nucleation and sintering characteristics of Co on ZnO(101虆0) during annealing were investigated by scanning tunneling microscopy (STM). The extent of coverage and annealing temperature were varied to modify the size of the Co nanoclusters. Temperature-dependent X-ray photoemission spectra of the Co chemical state reveal that metallic Co dominates the annealing procedure on ZnO(101虆0) and is more thermally stable than Co on both ZnO(0001) and ZnO(0001虆). The effects of annealing time and the distribution of Co adatoms were elucidated by STM. The results have potential implications for the thermal stability of Co/ZnO(101虆0) in real catalytic processes.