Alzheimer's disease (AD) patients exhibit various cognitive dysfunctions, including impairment of orientation for time (OT). The brain regions underlying OT impairment remain to be elucidated. A previous single-photon emission computed tomography study has indicated hypoperfusion of the posterior cingulate cortex (PCC) in relation to deterioration of OT. In this study, we investigated whole brain functional connectivity changes of PCC using resting-state functional magnetic resonance imaging. Voxel-based functional connectivity with PCC was analyzed in OT-poor or OT-good AD patients, classified according to the mean OT scores of the Mini-Mental State Examination subscale. The connectivities of dorsal frontal lobe, and lateral parietal and lateral temporal lobes with PCC in the right hemisphere were reduced in the OT-poor AD group compared with the OT-good AD group. A subtraction connectivity map of OT score differences (OT-good minus OT-poor) revealed the right middle temporal gyrus near the temporo-parietal junction as a significantly connected region with PCC. These results suggest that the right posterior part of the middle temporal gyrus may play an important role in OT in conjunction with PCC, and that disconnection between PCC and the right ventral attention network may cause OT disturbance in AD patients.