In our previous papers(l,2), it hae been reported that the genuine sapogenin of gineenoaidea-Rbl, Rb2, and Rc, the eaponine of Ginseng roots(3), can be represented by MS-protopanaxadio~=:20-epiprotopanaxadiol)(I)(4), and the partial etructure of these saponina can be formulated aa II. This communication deals with the structure of ginsenoside-Rgl(abbrev. Rgl), another saponin of this crude drug(3). Rgl. colourlese povder, mp 194-196.5: /ci/igo5 +32*(pgridine), haa been ieolated through ita deca-acetate(III), colourlees crystals, mp 242-243: /a/E405 +7.0* (CRC13), C42H72014(C2H20)10, molecular weight: Calcd. 1221.4, found by osmometry 1199.1, IR: no OH band. On hydrolysis with dil.mineral acid in aqueous ethanol, Rgl yielded E-glucose and panaxatriol(IV), whose structure has&ready been proved to be 6a-hydroxy-2OR-panaxadiol(4,5,6,7). On the analogy of the study on gineenoaides-Rbl, Rb2, and Rc(l), the mild hydrolysis of Rgl gave its genuine eapogenin, 20S-protopanaxatriol(=Q-hydroxj-20S-protopanaxadiol)(V)(7). Repeated methylation of Rgl with CR31 and DMSO-RaR reagent(2,E) gave an amorphous decamethyl ether(VI), IR: no OH band, m: signals due to -OCIi3(einglets) at 63.23(3H), 3.35(3R), 3.36(6H), 3.51(6R), 3.55(3H), 3.56(3H), 3.62(3R), and 3.63ppm: (T), signals due to -CIJ=C(Cg3)2 at 61.63(3R, singlet), 1.69(3R, einglet), and 5.06 ppm(lH, broad)(g), through an amorphous nonamethyl ether(VII), IR:$z4 3463cm-' (OH), NRR: signals due to -OC~3(singlets) at 63.38(9H), 3.53(68), 3.59(6H), 3.62