Abstract Background Conventional MRI techniques cannot demonstrate microvascular alterations in mild and moderate Alzheimer’s disease (AD). Thus, the diagnosis of microvascular pathology commonly relies on postmortem. The purpose of this study was to evaluate alterations of microvascular structures in patients with AD using a 3T clinical MRI system with a commercially available contrast agent. Method Eleven patients with AD and 11 non‐AD controls were included in this cross‐sectional prospective study. R2 and R2* relaxation rate changes (∆R2 and ∆R2*) before and after a Gd‐based contrast agent injection were calculated from images obtained with a multi‐echo turbo spin‐echo sequence and multi‐echo gradient‐echo sequence to obtain microvascular index maps of blood volume fraction (BVf), mean vessel diameter (mVD), vessel size index (VSI), mean vessel density (Q), and microvessel‐weighted imaging (MvWI). Two‐sample t‐test was used to compare those values between the two groups. Correlation analysis was performed to evaluate the relationship between those values and the mini‐mental state examination (MMSE) score. Result Compared with the non‐AD group, BVf was significantly increased in the AD group at the parahippocampal gyrus (p = 0.033), gray matter area (p = 0.008), and white matter area (p = 0.010). MvWI was also significantly increased in the AD group at the hippocampus (p = 0.010), parahippocampal gyrus (p = 0.010), precuneus (p = 0.045), and globus pallidus (p = 0.008). Both mVD and VSI were only significantly decreased in the AD group at the white matter hyperintensity (WMHI) area (p = 0.045 with mVD; p = 0.033 with VSI). BVf and MvWI were significantly positively correlated with age at some areas. VSI was significantly positively correlated with MMSE at caudate (rho = 0.475/ p = 0.030) and corpus callosum (rho = 0.435/ p = 0.049). Conclusion Microvascular index was a useful non‐invasive method to evaluate microvascular morphology alteration. The microvascular morphology of AD was manifested as vessel constriction and increasing blood volume fraction. It was associated with MMSE score.