Scutellariae Radix is widely used in the traditional herbal medicine for the treatment of fever, cough, dysentery, hepatitis and hypertension in Korea, China and Japan. In this study, we investigated the effects of 70% ethanolic extract of Scutellariae Radix (SRE) on CYP450-mediated drug metabolism in the in vitro systems using human liver microsomes and hepatocytes. The microsomal incubation assay showed that SRE inhibited the drug metabolism reactions catalyzed by CYP1A2, CYP2C8 and CYP2C9 in a dose-dependent manner. In particular, SRE was shown to strongly inhibit the metabolic activity of CYP1A2 with an $IC_{50}$ value of 4.6 ${mu}g/mL$. When SRE was evaluated for its effect on the induction of CYP450 enzyme activities in cryopreserved human hepatocytes, SRE did not exhibit any effect.