Abstract： Objective To evaluate the feasibility of the lateralization of unilateral medial temporal lobe epilepsy(mTLE)by using arterial-spin-labeling(ASL)based perfusion MR imaging and investigate the changes of perfusion in the regions related to mTLE network and the relationship between the perfusion and the clinical status.Methods Twenty-five patients with left-sided and 23 with right-sided mTLE were enroiled,and 30 healthy volunteers were recruited.The cerebral blood flow(CBF)of related region was measured based on pulsed-ASL sequence on Siemens 3 T scanner.The CBF of the mTLE group were compared with that in the controls by using ANOVA analysis.The asymmetric indices of CBF in the medial temporal lobe were calculated as the lesion side compared with the normal side in matched region in mTLE group.Results Compared with the volunteers,the patients with mTLE showed the decrease of CBF in the bilateral medial and lateral temporal,the frontal and parietal regions relating to the default-mode network and more serious in lesion side.The CBF values of the medial temporal lobe were negatively correlated with the epilepsy duration(r =-0.51,P ＜0.01).The asymmetric index of CBF as-0.01 has a 76.0％(19/25)sensitivity and a 78.3％(18/23)specificity to distinguish the lesion side.Conclusions The decrease of CBF in the temporal and extra-temporal region by ASL-based MRI suggests the functional abnormalities in the network involved by mTLE.The ASL technique is a useful tool for lateralizing the unilateral mTLE.