This study analyses the chemical composition and in vitro antioxidant activity of both the essential oil and the 80% aqueous acetone extract of Tetraclinis articulata leaves. The GC-MS analysis of the essential oil identified 66 components that comprise 93.5% of the oil. The major constituents of the oil are: bornyl acetate (31.4%), α-pinène (24.5%) and camphor (20.3%). Antioxidant activities of the samples were determined using four different test systems, namely DPPH, β-carotene/linoleic acid, reducing power and metal chelating activity assay. Test results from the DPPH system showed the strongest radical scavenging activity was exhibited by the 80% aqueous acetone extract (IC₅₀ = 5.5 µg mL⁻¹), which was two times higher than the positive control (BHT). The amount of the total phenolics, flavonoids and condensed tannins was very high in the 80% aqueous acetone extracts. The correlation between the antioxidant activity potential and total phenolic level of the extract was noted.