Graphene with its planar structure and exceptional mechanical and electrical properties has attracted a great deal of attention since 2004. Many researchers have tried to utilize this nanomaterial in different polymeric matrices to make high performance nanocomposites. However, the lack of hydrophilic functional groups on graphene surface and strong ð-ð interaction between graphene sheets restrict its dispersion in hydrophilic matrices, resulting in poor mechanical properties. The hydrophilic derivative of graphene, graphene oxide (GO), has high affinity to any hydrophilic matrices and improve mechanical properties of the resultant nanocomposite. On the other hand, cellulose nanofibers (CNFs) also have excellent properties such as high aspect ratio, high crystallinity, low density and high elastic modulus. Therefore, the objective of this work was to take advantage of superior properties of GO and CNF to make a new bio-based composite with exceptional mechanical properties. To study the mechanical properties of such composite, different samples containing 0.1 - 4 wt% of GO were prepared by vacuum filtration and characterized using Scanning electron microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction spectroscopy. Then, the mechanical properties of the resultant composites were investigated by tensile testing in 50% relative humidity. Results showed that by addition of only 0.1 wt% of GO to CNF, the modulus of the nanocomposite reaches to 16 GPa from 9,3 GPa for pure CNF and by adding more GO the modulus reaches a plateau and start to decrease. Comparison of microscopy and mechanical testing shows that the high modulus of the resultant composite is coming from the layered structure of the nanocomposite and the effective dispersion of GO that results in efficient stress transfer between GO and CNF.