This study aimed to evaluate the antioxidant potentials of aqueous extracts of four plants: Aloe ferox Miller, Zizyphus vulgaris lamk, Lawsonia inermis L. and Centaurium erythraea L. which are widely used in Algerian folk medicine for the treatment of gastroduodenal ulcers. Total phenolic, total flavonoid and tannins contents in the aqueous extracts were estimated. In vitro antioxidant activities were assessed by DPPH• radical scavenging assay, ferric reducing power activity, ferric thiocyanate (FTC) and thiobarbituric acid (TBA) methods. The in vivo antioxidant activities of these plants extracts were assessed using plasma antioxidant capacity, total proteins level, catalase (CAT), glutathione (GSH) and malondialdehyde (MDA) levels. Our results suggested that these plants aqueous extracts could be good sources of phenolic compounds and an ingredient with high antioxidant potential, and explain the traditional use of these plants in phytotheray.