Objective: To establish an ultra-high performance liquid chromatography method for the determination of mifepristone in the air of workplaces. Methods: From January to July 2018, glass fiber filter membrane was used to collect mifepristone in the workplace air, eluted with acetonitrile/water solution, and determined by ultra-high performance liquid chromatography-UV method. Results: The detection limit of mifepristone determination method was 0.005 μg/ml, the lower limit of quantification was 0.015 μg/ml, and the lowest detection concentration was 0.14 μg/m(3) (calculated by collecting 75 L air samples) . The concentration of mifepristone has a good linear relationship between 0.015-40.24 μg/ml, r=0.9999. The accuracy and elution efficiency of the method were calculated based on the recovery rate, ranging from 92.7% to 100.0%. The average sampling efficiency was 99.6%-100.0%. The intra-assay precision of the method was 0.92% to 5.41%, and the inter-assay precision was 0.89% to 6.25%. The sample could be stored stably for 3 days at 4°C. Conclusion: The ultra-high performance liquid chromatography method for determination of mifepristone is easy to operate, and its indicators meet the requirements of GBZ/T 201.4-2008 "Guidelines for the Establishment of Occupational Hygiene Standards Part 4: Methods for Determination of Chemical Substances in Workplace Air", which is suitable for the detection of mifepristone in the air of the workplace.