Abstract Background Previous studies reported increased concentrations of metallic ions and imbalanced Na+ and K+ ions in patients with Alzheimer’s disease (AD) and the increased mobility of protons by microstructural disruptions in AD. The purposes of this study were: 1)to apply a high‐frequency conductivity (HFC) mapping technique using a clinical 3T MRI system and 2)to compare HFC values among participant groups. Method This prospective study included 74 participants (23 AD patients, 27 amnestic mild cognitive impairment (MCI) patients, and 24 cognitively normal (CN) elderly people) to explore the clinical application of HFC mapping in the brain. For the brain MREPT images, a multi‐echo turbo spin‐echo pulse sequence was used. A homemade software was used to map the HFC at the Larmor frequency of 128 MHz at 3T. We performed statistical analyses to 1) compare HFC maps between the three participant groups and 2) to evaluate the association of HFC maps with Mini‐Mental State Examination (MMSE) scores. Result The HFC value was higher in the AD group than in the CN and MCI groups. MMSE scores were negatively associated with HFC values, but age was positively associated with HFC values. The HFC value in the insula has a high area under the ROC curve (AUC) value to differentiate AD patients from the CN participants (Sensitivity (SE) = 82, Specificity (SP) = 97, AUC = 0.902, p < 0.0001), better than GMV in hippocampus (SE = 79, SP = 83, AUC = 0.880, p < 0.0001). Conclusion HFC values were significantly increased in the AD group compared to the CN group and increased with age and disease severity. HFC values of the insula along with the GMV of the hippocampus can be used as an imaging biomarker to improve the differentiation of AD from CN.