The growth of metal-organic frameworks (MOFs) on a metal ion-doped polymer as a precursor and support substrate was investigated based on mechanistic and kinetic analyses. The studies were performed by varying the reaction temperature and the concentrations of the organic ligand and nucleation-promoted additive. Using the NH -MIL-53(Al) framework as a model system, a systematic study of the mechanism of formation of tetragonal-and rod-shaped NH -MIL-53(Al) crystals on the substrate was performed. The nucleation rate in the early stage of the reaction is a major factor in determining the surface morphology of the resultant NH -MIL-53(Al) crystal films, as confirmed by changing the concentration of organic ligands and by employing pyridine additives. These results provide a fundamental understanding of the influence of the nucleation rate on the ability to control the morphology and structure of MOF crystal films. 2 2 2