In patients with Moyamoya disease, posterior collateral circulation plays an important role in defending ischemic syndrome and good revascularization outcome. The association between bypassing perfusion and posterior collateral circulation remains unknown. This study thus used territory arterial spin labeling to evaluate the territory changes of these vessels. Our results showed that good bypassing perfusion is along with the improvement of posterior collateral perfusion territory. This indicates that good operation outcome was not only associated with poor collateral perfusion, but also related with good collateral vessels functioning as blood channels.