Proton magnetic resonance spectroscopy ((1)H-MRS) non-invasively provides in vivo biochemical information on tissue metabolites. In acute stage of cerebral ischemia, N-acetyl aspartate (NAA), one of (1)H-MRS observable metabolite, declines gradually reflecting energy impairment due to oxygen depletion. In our study, decline of NAA in ischemic core linearly correlated with the time from the onset of ischemia. Therefore NAA can be utilized to time clock biomarker for the acute stage cerebral ischemia.