Monoclonal antibodies Aducanumab, Lecanemab, Gantenerumab, and Donanemab have been developed for treatment of Alzheimer’s disease. Here, we have used single-molecule detection techniques and super-resolution imaging to characterise the binding of these antibodies to beta-amyloid aggregates including human post-mortem brain samples. Lecanemab is the best antibody in terms of binding to the small-soluble beta-amyloid aggregates, affinity, aggregate coating, and the ability to bind to post-translationally modified species, explaining its therapeutic success.