The properties of anodic oxide films on Au in lN HClO4 were studies as a function of time (2 sec to 5 min) and of potential of formation (1450 to 1850 mv vs. Pt, H2/H+ in the same solution). Over the range observed (10-20% of the total oxide), the oxide grows slowly with time, apparently according to Elovich kinetics, although the constants are potential-dependent. Oxides formed at longer times at a given potential are harder to reduce. This aging effect is greatest at the lower potentials of formation, despite the greater thickness of the oxide at the higher potentials and despite the larger change in the amount of oxide at the higher potentials. Because of these aging effects, the triangular sweep method of Will and Knorr is not suitable to study these films.