Protein adducts of the lipid peroxidation product 4-hydroxy-2-nonenal (HNE) are prominent features of oxidative damage in neuronal cell bodies in Alzheimer disease (AD). Such adducts are also seen in axons of normal as well as diseased individuals. These HNE adducts are constant throughout the axons and the aging process of humans, mice, and rats, indicating that HNE adduction is physiological and regulated from birth to senility. In axons, HNE is primarily adducted to the neurofilament heavy subunit (NFH) and the neurofilament medium subunit (NFM), and limited to lysine residues. Interestingly, we found that phosphorylation is essential since formation and removal of HNE adducts are controlled by the NFH/M phosphorylation state. Studies using immunochemistry, synthetic peptides, mass spectrometry and chemical stabilization of HNE adducts, demonstrated that XKSPX, the most repeated sequences in NFH/M, are the major component in neurons highly susceptible to phosphorylation regulated aldehyde adduction. To our knowledge, this is the first study to directly show phosphorylation can regulate NFH-HNE levels in axons and the multiple KSP repeats are the critical motifs which preserve the phosphorylation-dependent regulation. This study provides the new evidence that indicates signal transduction could modulate oxidative modification in brain through activation of kinases and phosphatases.