BACKGROUND: Scutellaria baicalensis is a perennial herbaceous plant widely distributed in Oriental areas. Its roots, a commonly used medicinal source, reputedly calm fetuses in pregnant women; however, there is no sufficient evidence to date to assess its safety during pregnancy. This study aims to evaluate the effects of S. baicalensis aqueous extract on embryonic development in ICR mice. METHODS: Aqueous extract of S. baicalensis roots was prepared in accordance with clinical application. Pregnant mice were randomly divided into four groups, i.e., mice treated by gavage with water as negative control, with aqueous extract of 2 (1.8 times of human daily dose), 8 or 32 g/kg/day from gestation day (Gd) 6 to 15 as low-, middle-, and high-dose groups, respectively. The parameters of live and dead fetuses, resorptions, external and skeletal malformed fetuses, maternal body weight, maternal liver, kidneys, and heart weights were evaluated on Gd 18. RESULTS: There was no significant difference in fetal parameters among four groups. Maternal absolute liver and kidneys weights in the high-dose group were significantly higher than those in negative control (p<0.05). Relative liver and kidneys weights in this group were significantly higher than those in any other group (p<0.05). CONCLUSIONS: Oral administration of aqueous extract of S. baicalensis roots at or below 32 g/kg/day to ICR mice during organogenesis did not cause significant fetal external or skeletal malformations. However, 32 g/kg/day presented potential maternal toxicity. Birth Defects Res (Part B)86: 79-84, 2009. © 2009 Wiley-Liss, Inc.