To optimize the lipophilicity and improve in vivo pharmacokinetics of near-infrared probes targeted Aβ plaques, we designed, synthesized, and evaluated a series of polyethylene glycol modified probes with hydroxyl and methoxyl terminals. The relationships between chemical structure and optical, biological properties were systemically elucidated. The results indicated that a desired Aβ probe should keep a balance among molecular rigidity, size, and lipophilicity. Probe 12d displayed improved properties including intense and selective response to Aβ1-42 aggregates ( Kd = 7.3 nM, 22-fold fluorescence enhancement and emission maxima at 715 nm upon interaction with Aβ1-42 aggregates), sufficient blood-brain barrier penetration (3.04% ID/g), and fast wash out from the brain (brain2 min/brain60 min = 10.1). Clear fluorescence signals retention in transgenic mice than control mice in in vivo near-infrared imaging. Hence, polyethylene glycol modified probes retained favorable optical properties but displayed great improvement of biological properties for Aβ detection.