A visible light-active, hematite-based photoelectrode platform for suppressing -amyloid (A) self-assembly in vitro is reported. Upon illumination of a light-emitting diode with an anodic bias, the hematite photoanode generates reactive radical species, such as superoxide ions and hydroxyl radicals, via photoelectrocatalytic process. According to our analyses, the hematite photoanode exhibited a strong inhibitory effect on A aggregation under visible light illumination and anodic bias. We found that hole-derived radicals played a significant role of oxidizing A peptides, which effectively blocked further aggregation. The efficacy of photoelectrocatalytic inhibition on A aggregation was enhanced by introducing cobalt phosphate (Co-Pi) as a co-catalyst on the hematite photoanode, which facilitated the separation of electron-hole pairs. We verified that both bare and Co-Pi@hematite photoanodes are biocompatible and effective in reducing A aggregation-induced cytotoxicity.