Natural polymers, used for hydrogel fabrication, are generally bioactive and provide good environment for cell growth and proliferation. However, these polymers have low mechanical strength. Several approaches have been attempted to improve their mechanical properties such as fabrication of interpenetrating polymer network (IPN) and semi-IPN hydrogels, and also addition of a nano sized fibers or nano-particles. The aim of this study was to investigate the feasibility of using naturally derived nano-fillers such as cellulose nanocrystallines to enhance the mechanical properties of hydrogels. Gelatin methacrylate (GelMA) was used as a protein model for preparation of photo-crosslinked hydrogel. The effects of concentrations of photo initiator and cellulose nanocrystallines (CNC) on the characteristics of hydrogels were examined. In vitro studies showed negligible cytotoxic effect of CNC on human osteosarcoma cell growth when using less than 20 mg/ml CNC. Therefore, it is viable to use this nano-filler for biomedical applications. It was found that the compression modulus of gelatin hydrogel was increased 1.5 fold by addition of 10 mg/ml of CNC. These results demonstrate the high potential of using CNC for tissue engineering applications to enhance the mechanical strength of hydrogels.