This study was designed to examine the chemical composition and in vitro antioxidant activity of the essential oil and various extracts of Haplophyllum robustum. GC-MS analysis of the oil resulted in the identification of 30 compounds, representing 99.2% of the oil; 1,8-cineole (38.1%), myrcene (10.7%), α-pinene (8.5%), 4-terpineol (7.0%) and sabinene (6.1%) were the main components. The antioxidant potential of the oil and extracts was evaluated using three separate methods: inhibition of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH), β-carotene-linoleic acid assay and reducing power systems. The essential oil of the plant was able to reduce the stable free radical DPPH with an IC₅₀ of 72.0 ± 1.2 µg mL⁻¹ (the IC₅₀ for ascorbic acid was determined as 5.8 ± 0.4 µg mL⁻¹). The essential oil also showed strong reducing power. The level of total phenolics was highest in the essential oil (179.5 ± 2.1 µg mg⁻¹).