Aluminum specimens were electropolished to five different roughness profiles and anodized in 10% oxalic acid under identical conditions in order to study the effect of surface topography on the thickness, morphology, chemical composition and hardness of the anodic aluminum oxide coatings formed. Field emission scanning electron microscopy showed that the anodic coating grown on a substrate having an average roughness of 250 nm was dense, whereas the microstructure became more porous with increasing the substrate roughness. The thickness of the coating was found to be a parabolic function of substrate roughness. Energy-dispersive x-ray analysis of coatings revealed a continuous increase in O/Al ratio with increasing substrate roughness suggesting increased incorporation of anions during oxide growth and also a tendency toward the formation of stoichiometric Al2O3. Coatings with higher O/Al ratio displayed improved hardness values.