The effect of basified modifiers in supercritical CO2 (SCF-CO2) such as diethylamine has been investigated on the SFE efficiencies of ephedrine derivatives (e.g. methylephedrine, norephedrine, ephedrine, and pseudoephedrine) from aerial parts of Ephedra sinica. The addition of basified modifiers in SCF-CO2 showed a greater enhancement of SFE efficiency of ephedrine derivatives than pure modifiers. These results might be due to the fact that the salts of Ephedra alkaloids (insoluble in CO2) in plant tissues would be changed to their free bases (freely soluble in CO2) by basified modifiers such as diethylamine in methanol. In addition to enhancing the solubilities, it could increase the degree of desorption of the compounds from plant matrix. Also, the SCF-CO2 modified with methanol basified with diethylamine showed a difference of extractability of ephedrine and its diastereomer, pseudoephedrine.