The antioxidant role of olive leaves obtained from Adana Topagi, Adana Yerli, Domat and Gemlik cultivars during olive ripening were investigated and compared to commercial olive leaf extract (OLE) as well as butylated hydroxyl toluene (BHT) and butylated hydroxyl aniline (BHA) as synthetic antioxidants. The results showed that total phenol contents of OLEs reduced 44 to 63% during ripening. OLEs, irrespective of cultivar and harvest date were found to be good sources of radical scavengers (P<0.05). The radical scavenging activity of OLEs at 100 or 200 mu g/g were higher than BHT (P<0.05) and similar or lower than BHA (P >= 0.05). The addition of Domat and Adana Topagi OLEs at 100 or 200 mu g/g to refined olive oil increased oxidative stability and caused to extracts to show better activity than commercial OLE but lower or similar activity than that of BHT and BHA (P <= 0.05) during different harvest times. BHA and BHT were the most effective antioxidants employed to delay the bulk oil oxidation but Domat and Adana Topagi olive leaves may have food additive value to slow down the progress of lipid oxidation and increase oxidative stability in refined olive oil. Due to concerns regarding the safety and toxicity of synthetic antioxidants, olive leaves may prove useful as safe, natural, functional ingredients with health promoting properties to food industry. Enrichment of oils or oil containing foods with the extracts from olive leaves and therefore, improving quality and healthiness of the target oils suggests a future possible use of them as a natural antioxidant and as an ingredient at an industrial scale since they seem to be useful for lipid stabilisation.