Abstract Zeolitic imidazolate framework (ZIF‐8) nanocrystals were uniformly grown on the surface of cellulose nanocrystals (CNCs) to give a hybrid material, ZIF@CNCs. By varying the stoichiometry of the components, it was possible to control the size of the ZIF‐8 crystals grown on the CNC surface. Optimized ZIF@CNC ( ZIF@CNC‐2 ) was used as a template to synthesize a microporous organic polymer (MOP), ZIF@MOP@CNC . After etching the ZIF‐8 with 6 M HCl solution, a MOP material with encapsulated CNCs ( MOP@CNC ) was formed. Zinc coordination into the porphyrin unit of the MOP yielded the ship‐in‐a‐bottle structure, Zn MOP@CNC , comprised of CNCs encapsulated within the Zn‐MOP. In comparison to ZIF@CNC‐2 , Zn MOP@CNC showed better catalytic activity and chemical stability for CO 2 fixation, converting epichlorohydrin to chloroethylene carbonate. This work demonstrates a novel approach to create porous materials through CNC templating.