Abstract: A simple, rapid and sensitive liquid chromatography-tandem mass spectrometry(LC-MS/MS) for the  determination of glycyrrhetic acid in human plasma with ginsenoside Rh2 as internal standard was developed and  validated. The plasma samples were prepared via liquid-liquid extraction with ethyl acetate. Chromatographic separation was accomplished on a Venusil MP-C18(50 mm?2.1 mm, 5 μm i.d.) column at 25 °C. The mobile phase consisted of acetonitrile/5 mmol·L–1 ammonium acetate(10:90, volume ratio) at a flow rate of 0.4 mL/min. Negative electrospray ionization was utilized as the ionization source. Glycyrrhetic acid and internal standard were determined via the mutiple reaction monitoring of precursor→production ion transitions at m/z 469→425, 409 and m/z 621→161, respectively. Each sample was chromatographed within 2.5 min. The lower limit of quantification was 0.50 ng/mL for 200 μL of plasma sample and the linear range was from 0.50 ng/mL to 800 ng/mL. The intra- and inter-day precisions were less than 8.76% in terms of relative standard deviation(RSD), and the accuracy was within a range of –3.25%—1.32% in terms of relative error(RE). The method was successfully applied to the pharmacokinetic studies of glycyrrhetic acid in healthy male Chinese volunteers after a single oral administration of 75 mg of glycyrrhizin.