Cellulose nanocrystals are sustainable nanomaterials commonly employed as biofillers in polymer composites. However, in their pristine state, they are incompatible with hydrophobic polymers. Thus, there is an ongoing research effort to enhance the compatibility and dispersion of CNCs in various polymer matrices to obtain their touted reinforcing potential. In this work, the formation of primary crosslinks of the CNC with epoxidized natural rubber (ENR) as well as the formation of secondary hydrogen bonds in a base-catalyzed reaction were studied at varying temperatures. The crosslink reaction was confirmed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. While the 180 oC treated ENR reinforced with CNC showed superior properties, all temperature-treated composites exhibited improved tensile strength and elongation at break. ENR - CNCs processed at 180 oC showed an 83 % increase in tensile strength compared to neat ENR. Toluene swelling tests confirmed the crosslinking of ENR-CNC composites treated at 180 and 220 oC. This was collaborated with a 342% increase in Mooney viscosity and an increase in the rheological properties. Overall, the catalyzed thermal treatment of ENR-CNC composite system generates covalent crosslinks between the CNCs and ENR that resulted in enhanced physico-mechanical properties. Such composites could be employed as a masterbatch filler for other hydrophobic rubbers, which can consequently enhance the compatibility of CNCs with the rubbers.