Oxidative stress is an important factor, and one that acts in the earliest stages, of Alzheimer's disease (AD) pathogenesis. The reduction of oxidative stress has been tested as a therapy for AD. While the trial of vitamin E supplementation in moderately severe AD is the most promising so far, it also reveals the limitations of general antioxidant therapies that simply lower oxidative stress and, therefore, the complexity of the redox system. The multiple contributing factors that foster the clinical manifestations of AD should be considered when designing antioxidative stress therapy. In this article, we discuss the multiple pathogenic mechanisms of oxidative stress in AD and the potential targeting approaches.