Chemical compositions and antioxidant activities of essential oils from nine different species of Turkish plants, namely Melissa officinalis L., Rosmarinus officinalis L., Cuminum cyminum L., Piper nigrum L., Lavandula stoechas spp., Foeniculum vulgare, Pimpinella anisum L., Thymus serpyllum and Liquidamber orientalis Mill., were studied. Essential oils were obtained by supercritical carbon dioxide (SCCO2) extraction and steam distillation, and were analyzed by gas chromatography-mass spectrometry. The antioxidant activities of SCCO2 extraction and steam distillation extracts were tested by means of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Essential oils extracted by SCCO2 and steam distillation showed different compositions in different species. In the DPPH assay, R. officinalis, C. cyminum, P. anisum, T. serpyllum and L. orientalis essential oils obtained by SCCO2 extraction showed higher antioxidant activity than steam distillation extracts, with radical scavenging activities ranging from 87.1 +/- 0.23% to 92.0 +/- 0.34% compared with the butylated hydroxytoluene positive control (91.4 +/- 0.21%).