To explore the application of arterial spin labeling magnetic resonance imaging (ASL-MRI) in the diagnosis and differentiation of presenile dementia. Methods: Total 13 patients with Alzheimer’s disease (AD) and 18 patients with frontotemporal dementia (FTD) were enrolled and assigned to the AD group and FTD group, respectively; 24 aged matched healthy elderly subjects and 22 healthy young subjects were enrolled and respectively assigned to the old control group and young control group. All subjects underwent ASL-MRI to quantify and analyze the cerebral blood flow (CBF) and volume of 10 gray matter regions. Sensitivity, specificity, and diagnostic performance assessments were performed in patients or patient groups and control groups with significant differences in cerebral blood flow. Results: Compared with that of the old control group, the perfusion of the anterior cingulate cortex in the FTD group was insufficient, and the AD group showed more extensive local hypo-perfusion and atrophy. Compared with that of the FTD group, perfusion of the posterior cingulate cortex in the AD group was insufficient. The differential sensitivity and specificity of the AD and FTD groups was 68% and 67% respectively; the differential diagnostic sensitivity and specificity of the AD and control groups was 76% and 75% respectively and that of the FTD and control groups was 78% and 74% respectively. Compared with the young control group, the old control group showed cerebral hypo-perfusion. Conclusion: ASL-MRI is helpful for the early diagnosis and differentiation of AD and FTD. Hypo-perfusion of the anterior cingulate cortex and posterior cingulate cortex can be used as a quantitative diagnostic marker for the diagnosis of Alzheimer's dementia and frontotemporal dementia.