Amyloid β 1–42 (Aβ_1–42) protein aggregation is considered one of the main triggers of Alzheimer’s disease (AD). In this study, we examined the in vitro anti-amyloidogenic activity of the isoindolinone derivative 3-(3-oxoisoindolin-1-yl)pentane-2,4-dione (ISOAC1) and its neuroprotective potential against the Aβ_1–42 toxicity. By performing the Thioflavin T fluorescence assay, Western blotting analyses, and Circular Dichroism experiments, we found that ISOAC1 was able to reduce the Aβ_1–42 aggregation and conformational transition towards β-sheet structures. Interestingly, in silico studies revealed that ISOAC1 was able to bind to both the monomer and a pentameric protofibril of Aβ_1–42, establishing a hydrophobic interaction with the PHE19 residue of the Aβ_1–42 KLVFF motif. In vitro analyses on primary cortical neurons showed that ISOAC1 counteracted the increase of intracellular Ca²⁺ levels and decreased the Aβ_1–42-induced toxicity, in terms of mitochondrial activity reduction and increase of reactive oxygen species production. In addition, confocal microscopy analyses showed that ISOAC1 was able to reduce the Aβ_1–42 intraneuronal accumulation. Collectively, our results clearly show that ISOAC1 exerts a neuroprotective effect by reducing the Aβ_1–42 aggregation and toxicity, hence emerging as a promising compound for the development of new Aβ-targeting therapeutic strategies for AD treatment.