Myelin ensheathment is essential for rapid axonal conduction, metabolic support and neuronal plasticity. In Alzheimer’s disease (AD), disruptions in myelin and axonal structures occur, although the underlying mechanisms remain unclear. We implemented proximity labeling subcellular proteomics of the myelin–axon interface in postmortem human brains from AD donors and 15-month-old male and female 5XFAD mice. We uncovered multiple dysregulated signaling pathways and ligand–receptor interactions, including those linked to amyloid-β processing, axonal outgrowth and lipid metabolism. Expansion microscopy confirmed the subcellular localization of top proteomic hits and revealed amyloid-β aggregation within the internodal periaxonal space and paranodal/juxtaparanodal channels. Although overall myelin coverage is preserved, we found reduced paranode density, aberrant myelination and altered paranode positioning around amyloid-plaque-associated dystrophic axons. These findings suggest that the myelin–axon interface is a critical site of protein aggregation and disrupted neuro-glial signaling in AD.