Electrochemical measurements combined with high resolution transmission electron microscopy studies have been used to follow the microstructure changes in nanoporous Au subjected to electro-oxidation and oxygen reduction reactions. The microscopy results reveal that different types of lattice defects such as stacking fault tetrahedra present in as-dealloyed and oxide formed nanoporous Au. It is shown that Au inter-planar spacing in the defect concentrated regions in as-dealloyed nanoporous Au has increased by 8%. This anomalous change may be attributed to the binding of oxygen containing ads-species in the electrolyte on Au atoms, albeit weakly, in the presence of defects.