Stroke is the first leading cause of death in China, and is responsible for almost 22.4% of deaths. In approximately 80% of cases stroke is ischaemic, i.e. caused by disruption of blood flow to part of the brain from an acute arterial occlusion. Survival of penumbral tissue distal to an arterial occlusion depends on collateral circulation via the Circle of Willis and leptomeningeal anastomises. Collateral flow is dynamic and failure is associated with infarct growth. The presence of adequate collaterals has been shown to be associated with age, history of statin use, and non-hypertension. Dl-3-n-butylphthalide (NBP), isolated from the seeds of celery, and found to exert protective effects against ischemic brain and increase leptomeningeal blood flow. This study investigate whether NBP injection prescribed during acute stroke will have a significant effect to improve collateral circulation in patients of anterior circulation occlusion.