The PV is a measurement of total peroxides, primary products formed in oils during the oxidation process. The effectiveness of an antioxidant in delaying the oxidation of oils can be assessed by a stable or a slower increase of a peroxide value compared to a control, in absence of phenolic extracts. shows that the RE can significantly reduce (p < 0.05) the frying oil oxidation during heating treatment. Before being subjected to heat, PV for control and rosemary treated oils were respectively 3 and 2.8 meq oxygen/kg. The peroxide value does not exceed 3.5 meq oxygen/kg in oil with added antioxidant. This value was reached after 18 h of heating. After 6 h of heating, the PV increase by about 100% in the control oil. This can be attributed to the polyinsatureted fatty acids oxidation and the hydroperoxides formation accelerated at high temperatures.