In Algerian traditional medicine, the old olive oils were used especially, to treat respiratory and digestive system diseases. This study aimed to evaluate the decomposition degree of three samples at different ages of olive oils. The analysis and identification of the fatty acids (FA) composition of samples were performed using the (GLC-MS). This analysis led to the identification of 16, 18 and 30 fatty acids. This increase in the number of fatty acids in the samples was especially in the saturated fatty acids, As noted a decrease in the value of some unsaturated acids like oleic acid (75.36% in sample 01, 75.48% in sample 02 and 48.31% in sample 03) and increase in values of saturated fatty acids as palmitic acid (12.59% in sample 01, 13. 75.32% in sample 02 and 29.22% in sample 03). Some physicochemical properties were determined (Density, Iodine, Peroxide, Saponification and Acid values). The values of these properties were changed according to the chemical composition of the samples
