Refined olive and refined soybean oils (RSO) have been analyzed in order to evaluate their physicochemical behavior during potatoes pan-frying. These refined oils exhibit significant variations in the physicochemical parameters when heated. A significant decrease (p<0.001) was practically observed in all analytical determination values except the induction time which showed a significant increase (p<0.001) with the enrichment with hydrolyzate olive leaf hydroxytyrosol-rich extract at 500 ppm during pan-frying. In fact, such enrichment has shown a remarkable resistance to oxidative deterioration, and the formation of trans-fatty acids (TFA) was found to be lower in the enriched refined oil samples during pan-frying. Such results have proven that not only is hydroxytyrosol-rich extract excellent antioxidant enrichment for refined olive and RSOs during pan-frying, but also it can be useful as substitute for synthetic ones. This study has shown that enriching refined oils with easily-found and cheap natural plant extracts could extend their usage life.Practical applications: The results of this research study have shown that refined pan-frying oils can successfully be enriched with hydrolyzate olive leaf hydroxytyrosol-rich extract at 500 ppm in order to enhance thermo-oxidative stability and reduce significantly the formation of trans-fatty acids. The hydrolyzate extract was found to be very suitable for this purpose. These materials are common agro-food by-products and can be produced very easily at a low cost. Besides, this type of enrichment may enable consumers to get some beneficial phenolic compounds through fried food consumption. In addition, these types of applications may open another area for marketing the named extract of natural origin.