Binary nano-biocomposite 3D scaffolds of cellulose nanocrystals (CNCs)—gelatine were fabricated without using chemical crosslinking additives. Controlled oxidative treatment allowed introducing carboxyl or carbonyl functionalities on the surface of CNCs responsible for the crosslinking of gelatine polymers. The obtained composites were characterized for their physical-chemical properties. Their biocompatibility towards different cell cultures was evaluated through MTT and LDH assays, cellular adhesion and proliferation experiments. Gelatine composites reinforced with carbonyl-modified CNCs showed the most performing swelling/degradation profile and the most promising adhesion and proliferation properties towards cell lines, suggesting their potential application in the field of tissue engineering.