AbstractUtilizing covalent organic framework (COF) as a hypotoxic and porous scaffold to encapsulate enzyme (enzyme@COF) has inspired numerous interests at the intersection of chemistry, materials, and biological science. In this study, we report a convenient scheme for one‐step, aqueous‐phase synthesis of highly crystalline enzyme@COF biocatalysts. This facile approach relies on an ionic liquid (2 μL of imidazolium ionic liquid)‐mediated dynamic polymerization mechanism, which can facilitate the in situ assembly of enzyme@COF under mild conditions. This green strategy is adaptive to synthesize different biocatalysts with highly crystalline COF “exoskeleton”, as well evidenced by the low‐dose cryo‐EM and other characterizations. Attributing to the rigorous sieving effect of crystalline COF pore, the hosted lipase shows non‐native selectivity for aliphatic acid hydrolysis. In addition, the highly crystalline linkage affords COF “exoskeleton” with higher photocatalytic activity for in situ production of H₂O₂, enabling us to construct a self‐cascading photo‐enzyme coupled reactor for pollutants degradation, with a 2.63‐fold degradation rate as the poorly crystalline photo‐enzyme reactor. This work showcases the great potentials of employing green and trace amounts of ionic liquid for one‐step synthesis of crystalline enzyme@COF biocatalysts, and emphasizes the feasibility of diversifying enzyme functions by integrating the reticular chemistry of a COF.