Hypertension (HTN) is one of the most common disorders and increases the risk of cardiovascular diseases (CVD), which are one of the main causes of death in the world. The Mediterranean diet has the efficacy to modulate CVD risk factors such as HTN, mainly because of olive tree products, which are the most pivotal ingredients in this diet. Among the olive tree products, olive leaf consists of many sorts of phenolic compounds and has several beneficial effects on human body, such as antioxidant, anti-atherosclerotic, anti-inflammatory and especially anti-hypertensive effects. So, we conducted a new systematic review and meta-analysis on anti-hypertensive effect of OLE in adults. The meta-analysis showed a significant reduction effect of OLE on systolic blood pressure. The anti-hypertensive effect of OLE is mainly considered due to its principal phenolic compound known as oleuropein (OL), which reduces blood pressure by a number of particular mechanisms associated with its specific chemical characteristics.