Phagnalon saxatile subsp. saxatile is a wild species very widespread in Algeria which is utilized for medicinal purposes as analgesic and anticholesterolemic. However, informations are still scarce regarding its phytochemical content. The objective of this study was to identify and quantify the phenolic compounds from different extracts of its leafy stems. For this purpose, the effects of four extracting solvents were investigated on the content of phenolic compounds and the antioxidant activity of this plant. Extracts prepared with polar solvents (methanol and water) contained higher amounts of phenolic compounds and showed better antioxidant activity than extracts with apolar solvents (hexane, dichloromethane). The methanolic extract, richest in total phenolic and total flavonoid, had significant antioxidant activity as regarded by DPPH° scavenging capacity (IC50 of 5.47 µg/mL), ABTS scavenging capacity (IC50 of 63.77 µg/mL) and inhibition of oxidation of linoleic acid (IC50 of 22.71 µg/mL), when compared to synthetic antioxidants. Chlorogenic acids and few flavonoids were identified and quantified by UPLC-DAD-MSn. The di-O-caffeoylquinic acids isomers were the most concentrated phenolics (25.4mg/g DW) in the methanolic extract.