Scutellariae radix, the root of Scutellaria baicalensis, is a traditional medicinal herb containing baicalin and wogonoside as the main flavonoids. Before absorption, these flavonoids are metabolized into their corresponding aglycones, baicalein and wogonin, by ${eta}$-glucuronidase produced by the intestinal microflora. To develop a method for efficient transformation of these flavonoids, optimal conditions for the production of ${eta}$-glucuronidase from Lactobacillus delbrueckii Rh2 (Rh2) were determined. Addition of 4% galactose to basal medium increased the enzyme activity of Rh2 by about 8-fold. Optimal pH and temperature for the ${eta}$-glucuronidase activity of cell extract were 5.0 and $50^{circ}C$, respectively, and more than 95% of the enzyme activity was maintained at $60^{circ}C$ for 11 h. Under optimal conditions, more than 90% of the glycones were converted into their corresponding aglycones within 3 h. These results demonstrate that the transformation of baicalin and wogonoside from S. baicalensis by Rh2 would be useful for the efficient production of wogonin and baicalein.