Acyl-coenzyme A: diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes triglyceride synthesis in the glycerol phosphate pathway. It has relations with the excess supply and accumulation of triglycerides. Therefore, DGAT inhibitors may act as a potential therapy for obesity and type 2 diabetes. Five flavonoids were isolated from the ethanol extracts of licorice roots, using an in vitro DGAT inhibitory assay. One isoprenyl flavonoid showed most potential inhibition of DGAT on five flavonoids (1-5). On the basis of spectral evidences, the compound was identified as glabrol (5). Compound 5 inhibited rat liver microsomal DGAT activity with an $IC_{50}$ value of $8.0;{mu}M$, but the $IC_{50}$ value for four flavonoids (1-4) was more than $100;{mu}M$. In addition, glabrol showed a noncompetitive type of inhibition against DGAT. These data suggest that potential therapy for the treatment in obesity and type 2 diabetes patients by licorice roots might be related with its DGAT inhibitory effect.