The possibility of preventing pitting corrosion of aluminum and aluminum-based alloys in marine environments by anodization was investigated. For six months, commercial-purity-grade aluminum and specimens of Alloys 3003 and 5083, which are frequently used in marine applications, were fully immersed in synthetic sea water and brackish water from the Huelva estuary. The behavior of sealed and unsealed anodized specimens is compared with that of unprotected specimens. Changes in the porous and barrier layers of anodized aluminum were studied by electrochemical impedance spectroscopy. Results were then compared with weight changes recorded during the exposure period and the specimen appearance at the end.