A reversed microemulsion electrokinetic chromatographic（MEEKC） method was developed for the separation of three corticosteroids，including hydrocortisone，prednisone and hydrocortisone acetate by using 1 butyl 3 methylimizolium tetrafluoborate（BMIM-BF4） ionic liquid（IL） as additive.The effects of experimental conditions such as BMIM-BF4 concentration and pH value on separation efficiency were investigated.The optimized conditions were as follows：24% sodium dodecyl sulfate（SDS），66% 1 butanol，05% n octane，35 mmol/L BMIM-BF4，pH 22 20 mmol/L NaH2PO4，an applied voltage of -20 kV and a detection wavelength of 250 nm.Under the optimized conditions，the calibration curves were linear in the range of 5-400,5-400,5-800 mg?L-1 for hydrocortisone，prednisone and hydrocortisone acetate with detection limits（S/N=3） of 09，09,12 mg/L，respectively.The RSDs（n=3） were less than 43%.The average spiked recoveries were 102%，97% and 94%，respectively.The results showed that the resolution of the IL-MEEKC method for the separation of hydrocortisone，prednisone and hydrocortisone acetate was higher than that of the conventional MEEKC method.The proposed method was simple，rapid and effective，and could be used for the quality control of cosmetics.