The flexural properties of ultrathin freely standing composite nanomembranes from reduced graphene oxide (rGO) and cellulose nanocrystals (CNC) have been probed by combining force spectroscopy for local nanomechanical properties and bulging test for global mechanical properties. We observed that the flexural properties of these rGO-CNC nanomembranes are controlled by rGO content and deformational regimes. The nanomembranes showed the enhanced mechanical properties due to the strong interfacial interactions between interwoven rGO and CNC components. The presence of weak interfacial interactions resulted in time-dependent behavior with the relaxation time gradually decreased with increasing the deformational rate owing to the reducing viscous damping at faster probing regimes close to 10 Hz. We observed that the microscopic elastic bending modulus of 141 GPa from local force spectroscopy is close to the elastic tensile modulus evaluated from macroscopic bulging test, indicating the consistency of both approaches for analyzing the ultrathin nanomembranes at different spatial scales of deformation. We showed that the flexible rGO-CNC nanomembranes are very resilient in terms of their capacity to recover back into original shape.