Abstract: In order to accurately determine the ergosterol in tobacco and tobacco products,a quantitative determination method by GC/MS with selected ion monitoring/full scan mode was established by taking 7-dehydrocholesterol as an internal standard and derivatizing before GC/MS analysis,and the contents of ergosterol in tobacco leaves and cigarettes of different kinds were determined. The results showed that the calibration curve exhibited good linearity with a correlation coefficient of 0.9995 in the range of 2.0 to 200.0 μg/mL. The LOD and LOQ were 0.46 and 1.53 mg/kg,respectively. The recovery ranged from 85.6% to 91.3%. This method is suitable for the quantitative determination of ergosterol in tobacco and tobacco products.