Alzheimer´s disease (AD) is a progressive and irreversible neurological disorder associated with age-related dementia. Extracellular deposition of fibrils derived from b-amyloid peptide (Ab) is one of the most important pathological hallmark of AD. Here we present results concerning the investigation of the in vitro inhibitory effect of the quinolones levofloxacin (3) and 3-carboethoxy-4-quinolone (4) on the Ab fibrillation. A b 42 peptide solutions were incubated in the presence of either compound 3 or 4 and the fibrillation was assessed by thioflavin-T fluorescence assay and atomic force microscopy (AFM). The results indicate that compounds 3 and 4 are inhibitors of Ab fibrillization, being the latter more potent. Quinolone 4 also promotes the disaggregation of pre-formed Aβ fibrils. We concluded that both compounds interfere with the fibrillization process.