The deposition of amyloid-β (Aβ) aggregates in the brain is a hallmark of the Alzheimer's disease (AD)-affected brain. Various aggregated Aβ species, including oligomers and fibrils, are generated upon the aggregation process, and these Aβ aggregates have distinct biological properties. To non-invasively monitor the aggregation pathways of Aβ and identify the existence of certain Aβ species in biological environments, an effective strategy to detect Aβ species is necessary. Herein, we report a turn-on near-infrared (near-IR) fluorescent probe, 1, for Aβ aggregates, which consists of a donor-π-acceptor system with an Aβ-interacting moiety. Our probe, 1, shows a noticeable increase in near-IR fluorescence at ca. 710 nm in the presence of Aβ aggregates in aqueous media. In addition, the fluorescent response of 1 was altered depending on the degree of Aβ aggregation. Moreover, 1 indicates turn-on fluorescence with Aβ aggregates in living cells and is nontoxic under the condition used for live-cell imaging.