Three dammarane types of saponins,including notoginsenoside R1,Rd and 20(S)-Rg3 were transformed using dodeca phosphotungstic acid.The chemical structures and transformation pathways of their products were analyzed by high performance liquid chromatography coupled with electrospray ionization multi stage mass spectrometry(HPLC-ESI-MSn).Totally,protopanaxatriol type saponin R1 was transformed into nine products,ie.20(S)-25-OH-R2,20(R)-25-OH-R2,25-OH-T5,20(S)-R2,20(R)-R2,20(S)-25-epoxy-R2,20(R)-25-epoxy-R2,T5 and 3β,12β dihydroxy 6α (2 O β D xylopyranosyl β D glucopyranosyloxy) dammar-20(22),24 diene,while ten identical products were obtained from protopanaxadiol type saponin Rd and 20(S)-Rg3,including 20(S)-25-OH-Rg3,20(R)-25-OH-Rg3,25-OH-Rk1,25-OH-Rg5,20(S)-Rg3,20(R)-Rg3,(20S,25)-epoxy-Rg3,(20R,25)-epoxy-Rg3,Rk1 and Rg5.Based on the structural identification,the relative content variations of major products with the reaction time were determined,and the transformation pathways for dammarane type saponin in acid solution were sequentially summarized.Results showed that dammarane type saponin could be readily transformed into rare ginsenosides via deglycosylation and epimerization reaction at C20 position,followed by hydration,dehydration and cyclization reactions on the olefin chain of dammarane type aglycone.