A simple method for the determination of ephedrine alkaloids: ephedrine (EF), pseudoephedrine (PE), norpseudoephedrine (NPE), norephedrine (NE) and methylpseudoephedrine (MPE) in dietary supplements by gas chromatography–mass spectrometry is described. After the addition of 3,4-methylenedioxypropylamphetamine as internal standard, a liquid–liquid extraction procedure in alkaline conditions with chloroform/isopropanol (9:1, v/v) was applied to the samples prior to analysis. Chromatography was performed on a fused capillary column and analytes, derivatized with pentafluoropropionic anhydride, were determined in the selected-ion-monitoring (SIM) mode. The method was validated in the range 0.3–10 μg/mg for EP, 0.06–2.5 μg/mg for PE and NPE and 0.04–1 μg/mg NE and MPE. Mean recovery ranged between 65.7 and 81.3% for the different analytes in dietary supplements. The quantification limits were 0.3 μg/mg for EP, 0.06 μg/mg for PE, 0.04 μg/mg for NPE, NE and MPE. The method was applied to analysis of various dietary supplements containing Ma-huang (Ephedra Sinica) and Sida Cordifolia plant extracts promoted for aiding weight control and boosting sports performance and energy.