Olive leaves and their extracts are associated with food preservation and health, and are used in folk medicine to treat several diseases, mainly because of their polyphenols. In this investigation polyphenols were extracted from olive leaves using green solvents and evaluated the antioxidant activity of the extracts. Polyphenols were extracted from fresh, freeze-dried, and hot air-dried leaves using either ethanol/water mixtures (70:30, 30:70, v/v) or water alone. Antioxidant activity was assessed in bronchial epithelial NCI-H292 cells by measuring reactive oxygen species (ROS) and in vegetable oil by measuring oxygen consumption. Results showed that extracts with a good antioxidant activity could be obtained when leaves were pre-treated by hot air-drying. The use of water alone as the extraction solvent gave results comparable to those obtained with ethanol/water (30:70, v/v). These extracts were particularly rich in oleuropein, and had anti-ROS effects in NCI-H292 cells and antioxidant activity in vegetable oil.