The objective of this study was to evaluate the polyphenol contents as affected by ripening of Kronaki, Chemlali, Frantoio and Mission olive varieties grown in the New Valley Governorate, Egypt. Besides, the effect of ripe Kronaki olive^'s total polyphenols addition on sunflower oil stabilityas natural antioxidants was evaluated. Total polyphenols content of virgin, crude pomace olive oils and vegetation water significantly increased from unripe to the ripe stage in all varieties. Kronaki fruits recorded the highest total polyphenols content followed by Frantoio, Mission and Chemlali in both two ripening stages. Total polyphenol contents were 315 and 335 ppm for virgin oil, 68 and 75 ppm for crude pomace oil and 230 and 250 ppm for vegetation water of Kronaki fruits at unripe and ripe stage, respectively. Polyphenol compounds of the studied virgin olive oils at ripe stage were determined by HPLC. p < /em>-coumaric acid was the predominant polyphenols compound represented 13.40, 11.53, 9.50 and 7.70 % followed by o-coumaric acid which recorded 5.98, 6.54, 8.78 and 7.37 % of total polyphenols in Kronaki, Mission, Frantoio and Chemlali, respectively. Moreover, gallic, catechin, p < /em>-hydroxybenzoic, salicylic, quercetin, cinnamic acids and phenol present as minor compounds in all studied olive oils. The stability of sunflower oil was increased with increasing the level of olive's polyphenols extract addition. Polyphenols extract addition at 0.15% exhibited remarkable antioxidant activity of sunflower oil and its stability reached to about two-folds compared with the control. Besides, the polyphenols extract from vegetation water was more effective on sunflower oil stability compared with that of virgin or crude pomace oil extracts. That encourages using the vegetation water (a by-product of olive oil industry) polyphenols extract as natural antioxidant source.