This study focused on characterizing the seed oil of Thapsia garganica (Apiaceae), a medicinal plant native to Laghouat, Algeria, and evaluating its antioxidant properties. Various solvent systems were employed to extract and fractionate the lipid content of T. garganica seeds oil. Chemical indices were determined, and fatty acids methyl esters were analyzed using GC/MS. Tocopherol composition was assessed via HPLC, and antioxidant activity was evaluated using the 2,2-diphényl 1-picrylhydrazyle (DPPH) method. The GC/MS analysis revealed distinct fatty acid profiles across various fractions, highlighting a notable presence of petroselinic acid and higher-than-usual levels of pentadecanoic acid in all fractions. T. garganica oil exhibited richness in tocopherols, particularly with α-tocopherol being the predominant homolog. The antioxidant activity assessment of different lipid fractions indicated potent activity within polar lipids (glycolipids and phospholipids). Furthermore, T. garganica oil was abundant in unsaturated fatty acids, notably petroselinic acid, displaying significant radical scavenging activity in its polar fractions. Keywords: T. garganica, petroselinic acid, pentadecanoic acid, tocopherols, antioxidant activity.