This paper reports a phytochemical study of the aerial parts of Astragalus monspessulanus L. growing in Algeria. It deals with the isolation and structure elucidation of 13 known compounds. From the n-butanol extract, seven flavonoids 1-7, two saponins and one lignan were isolated. In addition, two phytosterols and one triterpenoid were isolated from the ethyl acetate extract. The structures of all the isolated products were determined by using 1D and 2D-NMR techniques, measurement of optical rotation, mass spectrometry ESI-MS and by comparison with literature data. Furthermore, the antioxidant activity of the n-butanol extract of the aerial parts of Astragalus monspessulanus L. was investigated using the DPPH radical scavenging and ferrous ion chelating assays. The n-butanol extract showed low (EC 50 = 2.09±0.434 mg mL -1 ) to moderate (IC 50 = 63.60±0.01 μg mL -1 ) antioxidant activities depending on the test method.