BACKGROUND: Supercritical CO2 was utilised to extract Chinese star anise seed oil (CSASO), and a three-level Box - Behnken factorial design from response surface methodology was applied to optimise the extraction conditions, including pressure, temperature and amount of modifier (ethanol). The compositional analysis of fatty acids in CSASO was performed by HPLC with fluorescence detection using 2-(11H-benzo[a]carbazol-11-yl)-ethyl-4-methylbenzenesulfonate (BCETS) as labelling reagent. Identification was carried out by online atmospheric chemical ionisation-mass spectrometry. RESULTS: The optimum extraction conditions were as follows: extraction pressure, 27.72 MPa, extraction temperature, 46.22 degrees C, and amount of modifier, 8.58 vol.%. The experimental result showed that the maximum extraction yield was 25.31 +/- 0.22% (w/w) under the conditions proposed. The compositional analysis indicated that CSASO mainly contained C18: 2, C18 : 1, C18 : 3, C20 :4, C16, C18 and C20 fatty acids. CONCLUSION: In this study, a fast, simple and high-efficiency supercritical technique for extracting oil from Chinese star anise seed was developed. Simultaneous determination of fatty acids in CSASO using BCETS as the labelling reagent with HPLC fluorescence detection and online mass spectroscopy identification has been successfully achieved. (C) 2010 Society of Chemical Industry