Deep frying, one of the most common processes used for food preparation, is widely used by consumers and the food industry. Owing to the presence of oxygen, high temperature and water the frying process involves numerous reactions among which oxidation and polymerization stand out. This chapter is mainly focused on possibilities for preventing oxidation during the frying process with special attention to the influence of oil composition, i.e. degree of unsaturation, natural antioxidative compounds and additives, and frying conditions. Specific aspects of oxidation at high temperatures and low oxygen availability during the frying process, which contribute to modifying physicochemical, sensory and nutritional properties of oils, are reviewed. Also, the most important methods used for the evaluation of changes in oil quality are presented.