The present work has been carried out to ascertain the influence of different processing systems employed in olive process on the chemical composition, quality and stability of three Chemlali olive oils. Among these oils, two were classified as extra-virgin olive oils and the third named repassed olive oil was classified as an ordinary virgin olive oil. The analysis of the effect of the processing (two- and three-phases) on the analytical determinations values, revealed statistically significant differences (p<0.05) in some parameters, mainly in oxidative stability, antioxidant activity, total waxes, total phenols, o-diphenols and α-tocopherol contents as well as phenolic composition. The phenolic composition values were higher in the extra-virgin olive oil obtained from the two-phase system than in that obtained from the three-phase processing because it does not require the addition of water to the olive paste. Nevertheless, they were lower in the ordinary virgin olive oil (repassed olive oil) which was obtained by introducing hot water to the wet residues into the centrifugation processing at two-phases, than those in the extra-virgin olive oils obtained from the two- and three-phase processing.