The present invention relates to a method for selectively producing ginsenoside F2, compound Mc or compound O, which is originally present in ginseng in a trace amount, from a saponin of ginseng, and more specifically to a method capable of obtaining desired target compounds, that is, ginsenoside F2, compound Mc and compound O, in high yields, by treating saponins, obtained from ginseng, with particular enzymes to structurally convert the saponins.