This research aimed to evaluate for the first time the chemical composition and antioxidant potential of volatile fraction and different concentrates obtained from Acanthus mollis L.. The volatile components from the aerial parts of A. mollis were extracted by hydrodistillation and analyzed by GC-MS. Twenty-four compounds were characterized, representing 94.5% of the oil. The dominant compounds were hexahydrofarnesylacetone (52.4%), pulegone (15.0%) and spathulenol (4.5%), followed by appreciable amounts of menthone (2.8%), borneol (2.7%) and 2-hydroxy-5-methylacetophenone (2.0%). The Folin-Ciocalteu, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and ferric reducing antioxidant power (FRAP) assays were used to evaluate the total phenolic content and the antioxidant activity of plant extracts, respectively. Quantitative estimation of total phenols content by a colorimetric method showed that extracts were rich in these compounds, with a significant difference between samples. Total phenols varied from 0.0725 to 1.217 (mg GAE g^-1 dry weight). The percentages of DPPH inhibition were between 60.05 and 91.80%, while ascorbic acid gave 93.54%. The IC₅₀ values ranged from 3.066 to 3421 μg.mL^-1 for DPPH. The water extract of A. mollis was the most active (IC₅₀ = 3.066  ±  0.02 μg.mL^-1) compared to the other extracts. In addition, the volatile fraction of A. mollis exhibited a weak antioxidant capacity.