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Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory impairment and cognitive decline, ultimately culminating in dementia. This study aims to evaluate cerebrovascular reactivity (CVR) and functional connectivity (FC) in patients with AD and mild cognitive impairment (MCI) using resting-state functional magnetic resonance imaging (rs-fMRI), bypassing the requirement for hypercapnia. The study cohort comprised 53 AD patients, 38 MCI patients, and 39 normal control (NC) subjects. CVR is derived by extracting signals within specific frequency bands of rs-fMRI. This study compares the differences in CVR and FC among the three groups, using the brain regions with CVR differences as region of interest (ROI) for FC analysis. The correlation between CVR and FC and cognitive scale score was discussed. Compared with NC subjects, AD patients exhibited a decrease in CVR in the PCUN.L, whereas MCI patients showed an increase in CVR in the PCUN.R. With PCUN.L as ROI, FC in PCUN.R decreased in AD patients, and FC in SFGmed.R and other brain regions increased in MCI patients compared with NC subjects. The results of the correlation analysis indicate that CVR in all patients, as well as FC with the PCUN.L as the ROI to the PCUN.R and SFGmed.R, show positive correlations with MMSE and MoCA scores. These results suggest that there are significant differences between CVR and FC with CVR differential brain regions as ROI among the AD, MCI, and NC groups, which may help to explain the hemodynamic mechanism. CVR obtained with rs-fMRI may be a potential biomarker for assessing cognitive impairment., Competing Interests: Declarations. Competing interests: The authors declare no competing interests. Ethical approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study, and all experimental protocols were approved by the Ethics Committee of Zhejiang Provincial People’s Hospital (The People’s Hospital of Hangzhou Medical College) (No. 2012KY002)., (© 2024. The Author(s).)