Objective: To explore the effect of age on Qingkailing Granules disposition by comparing the pharmacokinetics of geniposide and baicalin in juvenile and adult rats.Methods: A simple and rapid LC-MS/MS method was developed and validated to simultaneously determine geniposide and baicalin in rat plasma after a simple protein precipitation.The analytes were separated on an Agilent ZORBAX Extend-C18 column.The mobile phase consisted of acetonitrile and water with 0.1％ (volume percent) formic acid at a flow rate of 0.6 mL/min.The ionization was conducted using an ESI source in negative ion mode.Multiple reaction monitoring was used for quantification at transitions of m/z 445.0 → m/z 268.9 for baicalin,m/z 433.2 → m/z 225.0 for geniposide,m/z 431.0 → m/z 341.0 for vitexin (IS).Juvenile and adult rats were administrated Qingkailing Granules (3 g/kg) orally.Plasma concentrations of baicalin and geniposide were determined by LC-MS/MS.Results: The linear ranges of the analytes were 1-1000 ng/mL for baicalin and 2-2000 ng/mL for geniposide.The method was successfully applied to compare the pharmacokinetics of the analytes between juvenile and adult rats after oral administration of Qingkailing Granules.AUC was bigger in adult rats,while t1/2 was longer in juvenile rats.Conclusion: These results suggested that the absorption and elimination of baicalin and geniposide in juvenile rats was lower than that in adult rats.Additional attention should be paid to the pharmacokinetic difference when Qingkailing Granules were used in children.