Numerous chemical reagents were developed for photodynamic therapy (PDT) since the ground breaking discovery that eosin can be used to treat skin tumors. Commercialized drugs, such as porfimer sodium (Photofrin), 5-aminolevulinic acid (ALA), methyl aminolevulinate (MAL), and methyl aminooxopenoat (MAOP), demonstrated the power of using light to target internal and skin tumors. In general, PDT relies upon generating reactive oxygen species (ROS) upon photoactivation that can damage lipids, proteins, and nucleic acids, eventually triggering cell death or protein inactivation. Recently, ROS-induced oxidative modifications of amyloid-β (Aβ) peptides have been recognized as an effective method for controlling their aggregation pathways that are directly linked to the pathology of Alzheimer's disease (AD). Oxidation of Aβ peptides with photosensitizers or redox-active molecules may alter their abnormal assembly and improve cognitive defects in AD transgenic mice. A variety of photosensitizers ranging from fullerene or porphyrin-based macromolecules, organometallic complexes, nanoparticles, and organic molecules were designed to modulate the aggregation of Aβ.