Abstract: The essential oil of Helianthus annuus head which harvested in autumn was extracted by water-steam distillation, and it's components was characterized by gas chromatography-mass spectrometry(GC-MS). The in vitro antioxidant activities of essential oil were studied by 2, 2-di(4-tert-octylphenyl)-1-picrylhydrazyl(DPPH) and 2, 2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS) radical scavenging assay. The GC-MS analysis showed 49 kinds of chemical components(comprising 91.16% of the essential oil) were identified from the essential oil of H. annuus head, and α-pinene(28.22%), limonene(6.55%), α-humulene(4.99%), trans-β-farnesene (3.58%) and camphene (3.39%) were the main ingredients. The essential oil had some in vitro antioxidant activity, and the half effective concentration(EC₅₀) of the essential oil against DPPH and ABTS radical were 0.47 and 0.30 g/L, respectively, which significantly higher than that of BHT(8.21 and 6.16 mg/L).