Tyrosine nitration of proteins at an extensive level is widely associated with the cognitive pathology induced by amyloid beta peptide (Abeta). However, the precise identity and explicit consequences of protein nitration have scarcely been addressed. In this study, we examined the detectable nitration of proteins in the hippocampus of mice with cognitive impairment (day 5) induced by the i.c.v. injection of Abeta(25-35) (day 0). The intensity of the nitration of proteins was inversely associated with the level of recognition memory in mice. The detectable tyrosine nitrations were revealed in proteins with a single size of approximately 70 kDa. The specific nitrated proteins at this size were identified using the liquid chromatography/mass spectrometry/mass spectrometry analysis and immunodetection methods. Intense nitration of the neurofilament light chain (NFL) was observed. The increased nitration of NFL was associated with its serine hyperphosphorylation and weak interaction with the nuclear distribution element-like, a protein essential for the stable assembly of neurofilaments. No changes in cell numbers in the hippocampus were found (day 5) in mice that received Abeta(25-35) injections. These findings suggested that extensive nitration of NFL is associated with the Abeta-induced impairment of recognition memory in mice.