Robust collateral circulation is strongly associated with better outcomes in acute ischemic stroke. In this prospective study, collateral circulation was defined as arterial transit artifact in Arterial Spin Labeling(ASL) images. Patients with ASL collaterals represented higher rate of good outcome and there were significant differences for percent changes of mRS score and NIHSS score between groups. Furthermore, the presence of ASL collaterals could predict good outcome, even after controlling for baseline NIHSS score. Taken together, ASL collaterals provide a powerful tool to predict clinical outcome for acute ischemic stroke with 90 days follow-up.