The marginal division (MrD) is a neostriatum subregion that links the limbic system and basal nucleus of Meynert; it is an important subcortical center that is involved in learning and memory. Alzheimer's disease (AD) is a neurodegenerative disorder and the most common cause of dementia in the elderly. AD clinically manifests as gradually progressive cognitive decline with behavioral disorders. Prior to full dementia, AD patients typically experience a transient state, i.e., mild cognitive impairment (MCI). Amnestic MCI individuals, but not all MCI individuals, frequently convert to AD dementia. To specify whether and how the functional relationships between the MrD and other brain regions change during AD, functional connectivity was assessed using resting-state functional MRI data and associated neuropsychological tests in AD and MCI patients (amnestic-type). Compared with normal controls, a different decreased functional connectivity pattern was observed between the MrD and caudate, the amygdala/parahippocampal region, the inferior frontal gyrus, the superior temporal gyrus, and the cerebellum for AD/MCI patients. Moreover, the functional connectivity between the MrD and the identified regions was significantly correlated with the neuropsychological scores among the MCI and AD subjects. Our results suggest that the MrD functional network is disrupted during AD.