Abstract: A rapid analysis method was established to identify ginseng and red ginseng. Ginsenosides in ginseng and red ginseng were studied as the fingerprint compounds by ultra-high performance liquid chromatography-electrospray ionization multistage tandem mass spectrometry (UPLC-ESI-MSⁿ). Power of ginseng sample was extracted with methanol at room temperature. The extract was centrifuged and filtered through a 0.22 μm filter before analyzed by UPLC-MS. UPLC separations were carried out using a BEH Shield RP₁₈ column (1.7 μm×2.1×50 mm, Waters ,USA) and a BEH RP₁₈ guard column(Waters). The column temperature was kept at 25 ℃. The flow rate was set to 0.3 mL/min， and the eluting gradient was as follows: acetonitrile (A) and water (B): 0—5 min, 25%—50%A; 5—8 min,50%—90% A; 8—10 min, 90%—100% A;10—12 min, 100%A. The injection volume was 10 μL. The detection wavelength was 195 nm. The mass spectrometer was operated in the negative ion mode with source voltage of 4.5 kV. The metal capillary voltage was 45 V, and temperature was 250 ℃. The sheath gas(N₂) flow-rate was 27 L/h, the auxiliary gas (He) flow-rate was 180 L/h. The scan range was m/z 200—1 500. Helium was used as collision gas, and collision energy was adjusted for the intensity ratio of the base peak to the parent ion between 2 and 20. The fragments got from ESI-MSⁿ supplied very important information to identify the ginsenosides. The data of the UPLC-ESI-MSⁿ for ginseng samples and red ginseng samples revealed that the chemical composition changes during the red ginseng steaming process. The result shows different batches of ginseng and red ginseng are clearly distinguished, which explain the chemical composition changes during the red ginseng steaming process. The method is rapid, simple, characteristic and good reproducibility.