A liquid chromatography–electrospray ionization-tandem mass spectrometry (LC–ESI-MS/MS) method was developed and validated for simultaneous determination of seven constituents including puerarin, daidzin, daidzein, paeoniflorin, albiflorin, liquiritin and liquiritigenin in rat plasma using schisandrin as the internal standard (IS). The plasma samples were pretreated by a one-step direct protein precipitation with acetonitrile. The chromatographic separation was carried out on a C18 column with a gradient mobile phase consisting of acetonitrile and water (containing 0.1% formic acid and 5 mM ammonium acetate). All analytes and IS were quantitated through electrospray ionization in positive ion multiple reaction monitoring (MRM) mode. The mass transitions were as follows: m/z 417.5 → 297.2 for puerarin, m/z 417.1 → 255.2 for daidzin, m/z 255.2 → 152.4 for daidzein, m/z 498.1 → 179.3 for paeoniflorin, m/z 481.1 → 197.3 for albiflorin, m/z 436.2 → 257.3 for liquiritin, m/z 257.2 → 137.3 for liquiritigenin and m/z 415.0 → 384.2 for IS, respectively. All calibration curves exhibited good linearity (r > 0.9979) over a wide concentration range for all components. The intra-day and inter-day precisions (RSD) at three different levels were both less than 14.3% and the accuracies (RE) ranged from −13.2% to 14.8%. The extraction recoveries of the seven compounds ranged from 72.9% to 117.4%. The validated method was successfully applied to pharmacokinetic study of the seven components in female rat plasma after oral administration of Ge-Gen Decoction aqueous extract.