Abstract: AimTo analyze the ginsenosides in Kou zi qi (rhizomes of Panax japonicus C.A.Mey. var. major (Burkill) C.Y.Wu et K.M.Feng), and to supply evidences for chemotaxanology of Panax species and clinical uses of Kou zi qi. MethodsThe ginsenosides were isolated by HPLC, then the positive- and negative-ion API-MS/MS of constituents collected from HPLC were measured. ResultsEight ginsenosides were identified as ginsenoside Re, ginsenoside Ro, chikuseksusaponins IV, IVa, notoginsenoside R₂, ginsenosides Rb₁, Rc and Rd, respectively, based on comparison of retention time with those of standards by HPLC, and analysis on their API-MS/MS data. Ginsenoside Ro and chikuseksusaponin IVa are the major components of Kou zi qi. ConclusionThis plant had a close relationship to P.stipuleanatus, P.zinginensis and P.japonicus var major; a relatively remote relationship to P.ginseng and P.quinquefolius, in a view of chemotaxanology. Ginsenoside Ro and chikuseksusaponin IVa might be the anti-inflammatory constituents of Kou zi qi.