Amnestic mild cognitive impairment (MCI) represents the early stage of Alzheimer’s disease (AD). Much research has focused on preventing the inevitable decline of MCI to AD. Aerobic exercise is considered a viable choice, and is shown to improve cognitive function in MCI. We focus on understanding the mechanisms that lead to this improvement. Pseudo-continuous-arterial-spin-labeling (PCASL) was used to assess resting cerebral blood flow (CBF) in two MCI groups. One group performed aerobic exercise, while another non-aerobic stretching. CBF was measured before and after training. CBF increase in the anterior-cingulate-cortex (ACC) was the proven mechanism that improves cognitive function in MCI.