Introduction: In healthy elderly persons and patients with mild cognitive impairment, physical exercise can increase functional brain connectivity in the default mode network (DMN) measured by resting-state functional magnetic resonance imaging (rs-fMRI). However, no studies have so far investigated the effect of physical exercise on functional resting-state connectivity in the DMN in patients with Alzheimer’s disease (AD). Objective: In a single-blinded randomized controlled trial, we assessed the effects of an aerobic exercise intervention of 16 weeks of physical exercise on DMN connectivity using rs-fMRI in patients with AD. Methods: Forty-five patients were randomly assigned to either a control or exercise group. The exercise group performed 60-min of aerobic exercise three times per week for 16 weeks. All the patients underwent whole-brain rs-fMRI at 3 T, at baseline, and after 16 weeks. Since the posterior cingulate cortex (PCC) and adjacent precuneus constitute a central hub of the DMN, this parietal region was defined as region-of-interest and used as the seed region for functional connectivity analysis of the rs-fMRI data treating age and gender as covariates. Results: Neither seed-based analysis, seeded in the PCC/precuneus region nor ICA-based analyses, focusing on components of the DMN network, showed any exercise-induced changes in functional resting-state connectivity from baseline to follow-up. Conclusion: 16 weeks of aerobic exercise does not modify functional connectivity of the PCC/precuneus region in patients with AD. A longer intervention may be needed to show the effect of exercise on brain connec-tivity. Clinical Trial Registration Number: The trial was registered at ClinicalTrials.gov (identifier: NCT01681602) on September 10, 2012.