Background: Adiantum capillus-veneris (Adiantaceae) is the only species of Adiantum genus growing in Iran. As a well-known plant in Iranian Traditional Medicine, to our knowledge, there has not been any report on essential oil constituents of this species as well as antioxidant activity evaluation of any plant belonging to Adiantum genus. Objectives: This study aimed to determine phytoconstituents of A. capillus-veneris volatile oil and its antioxidant activity. Materials and Methods: Essential oil obtained from arial parts of Adiantum capillus-veneris was analyzed by GC-Mass and its antioxidant activity was assessed by DPPH assay. Results: Analyses of yellow colored essential oil yielded 88.22% of total oil with 67 components. Among identified phytochemicals, carvone was the main component (31.58%). Moreover, percentage of carvacrol (13.75%), Hexadecanoic acid (5.88%), Thymol (4.05%), Hexahydrofarnesyl acetone (3.16%) and n-nonanal (2.99%) were more than other identified constituents. RC50 of this volatile oil was 0.039 mg/mL. Conclusions: Antioxidant activity of this essential oil could be somehow attributed to high contents of carvone, carvacrol and thymol. The volatile oil of this plant could have the potential of other biological activities, so further experimental investigations are recommended on this essential oil.