Alzheimer's disease (AD) is pathologically characterized by the formation of extracellular senile plaques, predominately comprised of aggregated β-amyloid (Aβ), deposited in the brain. Aβ aggregation can result in a myriad of distinct aggregate species, from soluble oligomers to insoluble fibrils. Aβ strongly interacts with membranes, which can be linked to a variety of potential toxic mechanisms associated with AD. Oxidative damage accompanies the formation of Aβ aggregates, with a 10-50% proportion of Aβ aggregates being oxidized in vivo. Hydrogen peroxide (H 2 O 2 ) is a reactive oxygen species implicated in a number of neurodegenerative diseases. Recent evidence has demonstrated that the H 2 O 2 concentration fluctuates rapidly in the brain, resulting in large concentration spikes, especially in the synaptic cleft. Here, the impact of environmental H 2 O 2 on Aβ aggregation in the presence and absence of lipid membranes is investigated. Aβ 40 was exposed to H 2 O 2 , resulting in the selective oxidation of methionine 35 (Met35) to produce Aβ 40 Met35[O]. While oxidation mildly reduced the rate of Aβ aggregation and produced a distinct fibril morphology at high H 2 O 2 concentrations, H 2 O 2 had a much more pronounced impact on Aβ aggregation in the presence of total brain lipid extract vesicles. The impact of H 2 O 2 on Aβ aggregation in the presence of lipids was associated with a reduced affinity of Aβ for the vesicle surface. However, this reduced vesicle affinity was predominately associated with lipid peroxidation rather than Aβ oxidation.