Olea europaea is an evergreen tree, native to the Mediterranean region and well known for its edible fruits and oil. Recently much focus has been made on the leaves of the trees due to their high antioxidant property in addition to other therapeutic value. The leaves that are considered by-products during olive oil production are now an essential commodity in the nutraceutical industry. Koroneiki (Olea europaea L. cv Koroneiki) is one of the well-known Greek olive cultivars as the queen of oil-producing olive trees. Our study focuses on studying this tree growing in Egypt in regards to its total flavonoids (TF) and phenolic content (PPh) as well as antioxidant activity in 2 seasons in a comparative presentation. The average PPh for Koroneiki leaf extract was found to be 116.81±0.97 and 152.98±0.11 mg/g dried extract for autumn and spring respectively while TF was found to be 48.32±0.5 and 82.68±0.71 mg/g respectively. In autumn the oleuropein content was found to be 12.65±0.06 mg/100 g dried extract, while in spring marked an increase in oleuropein content reaching 92.25±0.26 mg/100 g was observed. The % inhibition of the free radical for autumn extract was found to be 86.56 %±0.39, while 90.09%±1.18 for spring. The results indicated that spring is the season of choice for leaf collection.