Hierarchies design of porosity in metal‐organic frameworks (MOFs) has gained significant interest in recent years, and customization of mesoporous sizes in MOFs is still quite challenging. Herein, a template‐free method by nucleation‐competition has been developed to realize a near‐linear control of the mesopore sizes (3–13 nm) in the hierarchical MOF UiO‐66(Hf). High selectivity of enzyme adsorption, high activity of bulky‐molecular catalysis, high stability of mesostructure, and extension to other MOFs further prove the success in the potential customization synthesis and applications. A template‐free method by nucleation‐competition has been developed to realize near‐linear control of the mesopore sizes (3–13 nm) in the hierarchical metal‐organic frameworks UiO‐66(Hf), showing significant performances regarding molecular selectivity, catalytic activity, and mesostructure stability.