In this study, the strength of monolayer graphene oxide membranes was experimentally characterized. The monolayer GO membranes were found to have a high carbon-to-oxygen ratio (similar to 4:1) and an average strength of 17.3 N/m (24.7 GPa). This measured strength is orders of magnitude higher than previously reported values for graphene oxide paper and is approximately 50% of the 2D intrinsic strength of pristine graphene. In order to corroborate strength measurements, experimental values were compared to theoretical first-principles calculations. Using a supercell constructed from experimental measurements of monolayer graphene oxide chemistry and functional structure, density functional theory calculations predicted a theoretical strength of 21.9 N/m (31.3 GPa) under equibiaxial tension, in good agreement with the experimental data. Furthermore, computational simulations were used to understand the underlying fracture mechanism, in which bond cleavage occurred along a path connecting oxygenated carbon atoms in the basal plane. This work shows that monolayer graphene oxide possesses near-theoretical strength reaching tens of GPa.