Abstract: After the sample was ground and mixed well, 0.050 0 g of the sample was ultrasonically extracted with 10 mL of methanol for 10 min. After standing, the supernatant was taken and filtered through a 0.22 μm microporous membrane. The filtrate was diluted with methanol. Sibutramine, phenolphthalein, fenfluramine, caffeine and ephedrine in the solution were determined by ion mobility spectrometry. The optimized conditions for determination were as follows:ion source voltage of 2 550 V, drift tube voltage of 7 350 V, drift tube temperature of 180℃, drift gas flow rate of 1.5 L·min^-1, and exhaust flow rate of 0.8 L·min^-1. Linear relationships between values of peak area and mass concentration of the five kinds of illegal additives were found in the same range of 0.10-20 mg·L^-1, and detection limit (3S/N) were in the range of 0.05-0.10 mg·L^-1. Values of recovery obtained by standard addition method were between 71.9% and 91.3%, and RSDs (n=6) were less than 10%. The method was used to determine the above five illegal additives in 6 kinds of commercially available weight loss health care products. Phenolphthalein was detected in one sample, with the mass ratio of 3.1 mg·g^-1; caffeine was detected in other two samples, with the mass ratio of 1.6, 41.6 mg·g^-1, respectively.