Objective To analyze the high-resolution magnetic resonance imaging (HR-MRI) findings of middle cerebral artery (MCA) vessel wall for Moyamoya disease (MMD) and atherosclerotic Moyamoya syndrome (AS-MMS), and to explore the diagnostic value of HR-MRI for MMD. Methods We selected 24 MMD patients (MMD group) and 24 AS-MMS patients (AS-MMD group) from Changhai Hospital.HR-MRI comparison was made for the difference between the two groups concerning the ages and risk factors, including episode style, history of diabetes, hyperlipaemia, hypertension and stroke. 3.0T HR-MRI enhanced scanning was performed for MCA vessel wall changes in all patients.Then the inner and outer diameters of MCA, wall thickness, signal intensity of vessel wall, enhancement effect, microvascular adjacent to MCA and its remodeling index (RI) were analyzed. The outer diameters of two groups were analyzed by the receiver operating characteristic (ROC) curve. Results We found that ages and risk factors were significantly different between the MMD and AS-MMS groups (P<0.05). The MCA outer diameter was significantly smaller in MMD group than that in the AS-MMS group ([2.70±0.44] mm vs[3.31±0.54] mm, P<0.05), but the wall thickness was significantly thicker than that in the AS-MMS group ([1.99±0.32] mm vs[1.39±0.57] mm,P<0.05).The focal enhancement of MCA arterial wall in AS-MMS group was more commonly seen than that in MMD group (50.00% vs 33.33%, P<0.05). Compared with AS-MMS group, the RI in MMD group was mostly negative remodeling (79.17% vs 25.00%, P<0.05), with the average RI significantly decreased ([0.86±0.12] vs [1.05±0.21], P<0.05) and the occlusion incidence of microvascular adjacent significantly increased (83.33% vs 24.17%, P<0.05). ROC curve showed when the threshold value of MCA outer diameter was 3.13 mm, the differential diagnosis had a 90.7% sensitivity and a 64.0% specificity. Conclusion HR-MRI has an important value for differential diagnosis of MMD and AS-MMS.The arterial wall of MCA in MMD patients undergoes shrinkage and negative remodeling. The outer diameter is often less than 3.13 mm with concentric stenosis, and the arterial wall has no enhancement or concentric enhancement, with microvascular adjacent to MCA more commonly seen in MMD group.