A new generation of carbon-based materials such as graphene and graphene oxide (GO) have been widely studied due to their potential in a variety of applications including biomedical materials and devices. This work investigates the appropriate GO morphology and content to be used as a filler for a poly(carbonate urethane) (PCU) polymer in order to mechanical properties improvements. Two graphene oxides with different levels of oxidation and morphology were blended into a PCU matrix to obtain high mechanical performance and good flexibility. Nanocomposites of PCU and GO were produced with a filler content of 0.2 wt%, 0.4 wt%, and 2.0 wt%. Polymeric membranes were obtained using solvent evaporation and characterised by their thermal properties (Differential Scanning Calorimetry), thermo-mechanical (Dynamic-Mechanical Thermal Analysis), and mechanical test results (tensile). The results indicated that GO platelets tend to interact strongly with the hard segments (HS) of PCU chains due to the polar chemical similarity of GO and HS structures. Two mechanical behaviours were found for the PCU/GO-2 nanocomposites, at small and large deformations. Improvements in the Secant Modulus and values of stress until 350% of strain are observed for low filler content while high filler content is needed for improvements at break point (stress and strain). PCU/GO nanocomposites with high mechanical performance can be produced by adjusting the GO content and characteristics to reach different application possibilities.