Medicinal plants constitute an inexhaustible reservoir of the most effective folk remedies thanks to the valuable bioactive compounds they contain. The present work is based on the phytochemical study and the dosage of some phenolic compounds (flavonoids, polyphenols) as well as the evaluation of the antioxidant activity (anti-radical activity DPPH, anti-radical activity ABTS) of the three Saharan and Mediterranean plants Matricacia pubescens, Salvia verbenaca and Santolina africana. They are used in traditional Algerian medicine. The phytochemical screening made it possible to highlight the presence of flavonoids and tannins in all the extracts of the three plants. These compounds are well known for their beneficial health properties, particularly due to their anti-inflammatory, antimicrobial and antioxidant effects. The total phenolic and flavonoid contents were estimated using the Folin-Ciocalteu reagent and the aluminum chloride reagent respectively. The antioxidant and free radical scavenging activity was determined by several standard methods using a spectrophotometer (DPPH• anti-radical activity, ABTS•+ anti-radical activity). Evaluation of the content of phenolic compounds shows the richness of S.verbanaca in flavonoids and polyphenols with contents 25.17 ± 0.02 mg EQ/g of extract, 72.80 ± 0.02 mg EAG/g of extract respectively. The results of this study highlight the importance of phenolic compounds, in particular flavonoids, in the antioxidant properties of the Saharan and Mediterranean plants studied. Salvia verbenaca, with its high levels of flavonoids and polyphenols, stands out particularly for its high antioxidant potential. Statistical analysis reveals the existence of a correlation between the content of antioxidants (flavonoids, polyphenols) and antioxidant activity .These results confirm the traditional use of these plants in Algerian folk medicine and suggest their potential for the development of new natural therapeutics based on their bioactive extracts.