A mixture of 20(R)- and 20(S)-ginsenoside Rg$_{3}$ was obtained under mild acidic hydrolysis from protopanaxadiol saponins, ginsenosides Rb$_{1}$, Rb$_{2}$, Rc and Rd. The product was acetylated to give the peracetates, which were further converted into 20(R)-ginsenoside Rg$_{3}$, 20(S)-ginsenoside Rg$_{3}$, 20(R)-ginsenoside Rh$_{2}$ and 20(S)-ginsenoside Rh$_{2}$ by the direct alkaline treatment depending upon two kinds of temperature conditions respectively. The structure and physicochemical properties of a prosapogenin, 20(R)-ginsenoside Rh$_{2}$, were investigated.