Hydroxylamine (HA), a reactive nitrogen species generated by neuronal nitric oxide synthase (nNOS), has been largely overlooked in neurodegenerative disorders. Herein, we report the first identification of HA overexpression in Parkinson's disease (PD) and elucidate its pathological role using chemo-selective fluorescence imaging combined with proteomic analysis. A general HA-responsive probe platform was developed by introducing a 1-(4,4-dimethyl-2,6-dioxacyclohexylidene)ethyl (Dde) unit as a highly specific HA-recognition motif. Among the resulting probes, DCI-HA-2 exhibited remarkable sensitivity, a fast response, and excellent selectivity toward HA. Using DCI-HA-2, elevated HA levels were visualized in PD cells, PD model mice, and brain tissues for the first time. Mechanistically, nNOS-derived HA suppresses cystathionine β-synthase (CBS) expression, leading to impaired hydrogen sulfide (H2S) biosynthesis, and simultaneously induces adenosine-5'-triphosphate (ATP) depletion, thereby disrupting adenosine 5'-monophosphate-activated protein kinase (AMPK) signaling in PD pathology. This work identifies HA as a previously unrecognized pathological regulator in PD, and establishes a powerful chemical strategy for probing HA-associated pathological processes in complex biological systems.