Abstract: OBJECTIVE To establish a method for quantitation of free hydrogen cyanide in Jian’er Qingjie mixture by headspace gas chromatography.METHODS The assay was performed on an Agilent PLOT-Q capillary column(30 m×0.32 mm, 40 µm) combined with an oven temperature program. The GC injection port was maintained at 200 ℃ and the split ratio was 5∶1. The temperature for FID detector was set at 300 ℃. Samples were incubated at 50 ℃ for 30 min before headspace sampling and injection according to the stability evaluation of mandelonitrile which the unstable coexisting precursor of hydrogen cyanide by HPLC after incubation under different temperature conditions. The standard curves were prepared using 0.10 g·mL^-1 sodium chloride solution as surrogate matrix to overcome matrix effects. RESULTS The linear range of hydrogen cyanide was 0.519-20.775 µg·mL^-1(r=1.000 0). The average recovery was 96.7% with RSD of 2.6%(n=9). The relative deviation of the measurement results of the alternative matrix standard curve method and the standard addition method was <7%. The content range of free hydrogen cyanide in the 10 batches of Jian’er Qingjie mixture produced by 5 manufactures was 0.653-16.540 µg·mL^-1. CONCLUSION The established method is simple, accurate and reproducible. It can be useful for the quality control and safety evaluation of Jian’er Qingjie mixture.