Ginsenosides have poor oral bioavailability and undergo rapid biological transformation in the complex gastrointestinal environment. Most studies on the metabolism of ginsenosides have focused on gut bacteria, yet gastric juice remains a nonnegligible factor. Metabolic profiles of ginsenoside monomers formed in artificial gastric juice were separately investigated and qualitatively identified using ultra-high-pressure liquid chromatography coupled with linear ion trap-Orbitrap mass spectrometry (UHPLC-LTQ-Orbitrap MSn). A common pattern of their metabolic pathways was established, showing that ginsenosides were transformed via deglycosylation, hydration, and dehydration pathways. Two major structure types, 20(S), 20(R)-protopanaxatriols and 20(S), 20(R)-protopanaxadiols, basically shared similar transformation pathways and yielded deglycosylated, hydrated, and dehydrated products. Fragmentation patterns of major ginsenosides were also discussed. Consequently, gastric juice, as the primary link in ginsenoside metabolism and as important as the intestinal flora, produces considerable amounts of degraded ginsenosides, providing a partial explanation for the low bioavailabilities of primary ginsenosides.