To analyze scientifically the prescription principle of polyprescriptions (Gamchotang, Daewhanggamchotang, Jakyakgamchotang, Gamchogungangtang and Gilkyungtang) containing Glycyrrhizae Radix, the transforming rate of glycyrrhizin in these polyprescriptions to 18 ${eta}-glycyrrhetinic$ acid and their inhibitory effect on ${eta}-glucuronidase$, hyaluronidase, phosphodiesterase and trypsin were investigated. When Glycyrrhizae Radix containing polyprescriptions were extracted with water, the contents of glycyrrhizin in water extract of Glycyrrhizae Radix with Rhei Rhizoma or with Zingiberis Rhizoma were higher than that of Glycyrrhizae Radix only, but that in water extract of Glycyrrhizae Radix with Platicodi Radix was lower than that of Glycyrrhizae Radix only. By human intestinal bacteria, glycyrrhizin was metabolized to 18 ${eta}-glycyrrhetinic$ acid. These metabolism of glycyrrhizin in polyprescriptions containing Glycyrrhizae Radix was inhibited by Rhei Rhizoma, Paeoniae Radix and Platicodi Radix, but was not affected by Zingiberis Rhizoma. The inhibitory activity of Glycyrrhizae Radix on hyaluronidase and ${eta}-glucuronidase$, was synergistic with Rhei Rhizoma or Zingiberis Rhizoma, but was antagonistic by Platicodi Radix.