Abstract： Objective To explore the feasibility of 256-slice whole-brain CT perfusion (CTP) in evaluate graft reperfusion after surgical revascularization and hemodynamic alterations before and after surgery in Moyamoya disease. Methods Twenty-five cases with Moyamoya disease were scanned on a 256-slice CT.CTP was performed pre- and post- surgical revascularization. The wolumetric CT angiographic ( CTA ) images were generated from volumetric data acquired at the arterial phase of CTP. CBF, CBV, TTP and MTT were measured in functional maps at the operated side within middle cerebral artery perfusion areas and contralateral mirroring areas. Relative CBF( rCBF), relative CBV (rCBV), relative TTP (rTTP), relative MTT (rMTT) were also obtained. Differences in perfusion CT values pre- and post operation were assessed with the paired t test or matched-pairs signed-ranks test. Data with normal distribution was present as : (x-)± s,while those with the non-normal distribution were present as M ( P25-P75 ). Results All the direct graft patencies were displayed on volumetric CTA. No significant differences were found between volumetric CTA and conventional CTA. Postoperative CBF, rCBF and rCBV values of the operated side [ 72. 86 (55.54-112. 19) ml · 100 g-1 · min-1 , 1. 31 ( 1.05-1.73), 1.45 ±0. 62] were significantly higher than those before operation [46.72(28.57-57.67) ml · 100 g-1 · min-1, 0.53(0.33-0.82), 1.01 ±0.36](Z=- 2.72, - 2. 98, t = - 2. 85, P ＜ 0. 05 ). Postoperative MTT, TTP and rTTP values of the operated side [ (3.98 ± 2. 36 ) s, ( 17.56 ± 4. 38 ) s, 1.01 ± 0. 09 ] were significantly lower than those before operation [(5.43±2.07) s,(19.40±3.87) s,1.14±0.28] (t=2.41,2.17,2.17, respectively, P＜0.05).However, no significant differences were detected for changes of CBV and rMTT after revascularization ( P ＞0. 05). Conclusion 256-slice CT has the potential value for the non-invasive assessment of both the graft patency and cerebral hemodynamics changes in moyamoya disease after surgery with administration of one contrast medium bolus in a single examination.