BACKGROUND/AIMS Amnesic mild cognitive impairment (aMCI) is thought to represent a transitional state between healthy aging and very mild Alzheimer's disease (AD). It is very important to diagnose aMCI for early treatment. In order to investigate biochemical changes in aMCI, we measured metabolite concentrations using proton magnetic resonance spectroscopy ((1)H-MRS) from patients with aMCI and compared the results with healthy controls (HCs) and patients with AD. METHODS The subjects were 52 HCs, 70 AD patients and 47 aMCI patients. (1)H-MR spectra with single-voxel point-resolved spectroscopy at a short echo time (TE) were acquired from 8 volumes of interest in the brain. RESULTS The bilateral hippocampal N-acetylaspartate (NAA) concentrations from aMCI patients showed intermediate values, which were lower than those from HC subjects but higher than those from AD patients. The patients with aMCI also had lower concentrations of NAA than HCs in the bilateral posterior periventricular and deep white matters (PDWM) and posterior cingulate gyrus and had lower levels of choline compounds in the left posterior PDWM. CONCLUSION Using a single-voxel (1)H-MRS at a short TE, we revealed that absolute quantification is useful to detect the characteristic patterns of metabolite concentrations in patients with aMCI as compared with AD patients and HCs.