A B S T R A C TBackground: Achillea wilhelmsii (Asteraceae) is a Permanent herb, belongs to the genus Achillea (Compositae) Which grows wild in some regions of Iran including Taftan area of Sistan and Baluchestan, in southeast of Iran. Objectives: The purpose of this study was to determine the comparative chemical composition and antioxidant activities of the essential oils extracted from the flowers, stem and leaves of Achillea wilhelmsii. Material and Methods: In this study, the chemical composition of essential oils of the flower and stem of Achillea wilhelmsii from Taftan were obtained by the hydrodistillation method and analyzed by gas chromatography and gas chromatography mass spectroscopy. Results: Sixty one compounds were identified in the essential oil of the flower. The major compounds were Camphor (27.99%), Sabinyl acetate (6.56%), Terpinene-4-ol (6.43%) Camphene (6.43%) and Alpha-Pinene (5.47%). Forty eight compounds were identified in the essential oil of the stem and leaves, which the major compounds were Camphor (34.49%), Alpha-Pinene (8.16%), Camphene (7.87%), Terpinene-4-ol (5.70%), 1,8-Cineole (3.32%). In addition, the antioxidant activity of ethanolic extract was evaluated using the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method. Conclusions: According to antioxidant activity outcomes, the amount of IC50s of aqueous extracts of flower and stem and also butylated hydroxyl toluene (BHT) as standard were 232.34, 63.25 and 45.59 ppm respectively. Ultimately, it was highlighted that antioxidant activity of aqueous extract of flower was weaker than stem.