Backgroud Rhizoma Atractylodis Macrocephalae (RAM) is the dried rhizome of Atractyledes macrocephala Koidz in the Compositae family.It is a commonly used tonic herb in China in the treatment of diarrhea,lack of apperite,anorexia,mental fatigue and other symptoms.This herb has also been used for thousands of years to treat pregnant disorders for preventing abortion during early pregnancy.However,there is no sufficient evidence so far to identify its embryotoxicity and teratogenicity.Objective This study aimed to (1) evaluate the safety of the aqueous extract of RAM on embryonic stem cells (ESCs),pregnant mice and their fetuses,(2) compare the effects of RAM extract at different doses,and between RAM extract with vitamin A,a well known teratogen in mice.Method RAM was quantitatively authenticated by HPLC analyses.In in-vitro studies,ESCs and 3T3 cells were cultured and IC50 values of aqueous extract of RAM were measured in a cytotoxicity assay.Meanwhile,in-vivo studies (Segment Ⅱ study) were processed,and pregnant mice were randomly divided into 5 groups,i.e.,pregnant mice were treated orally with distilled water as negative controls (G1,n =17),with aqueous extract of 2,8,32 g/kg/day as low-,middle-,and high-dose groups respectively (G2,n =18;G3,n =18;G4,n =17)from the Gestation Day (GD) 6 to 15,and vitamin A of 200,000 IU/kg at the GD 7,9,11 as positive controls (G5,n =17).The percentages of resorpted embryo and dead fetus (RD%),apparent malformed fetus (AM%) and skeletal abnormal fetus (SA%),the maternal increased whole body weight (WW),uterus-free weight (UW) and liver,kidney and heart weight ratios (LW% ,KW% and HW%) were measured on the GD 18.Result (1) Phytochemical analyses showed that the concentration of atractylolide in RAM water extract was 105 ? g/g,and it was reached the required quality standard.(2) Cytotoxicity analyses showed that the inhibition of cell viability of cultured ESCs and 3T3 cells was in a dose-response manner,IC50 ESC was 7.518 ±1.205 (n =4),IC50 3T3 was 3.166 ± 1.088 (n=4),and IC50 ESC was significantly higher than IC50 3T3 (P=0.02).(3) Fetal evaluations showed that the RD% ,AM%,SA% in G5 were 55.07%,46.08% and 48.04%,which was significantly higher (P < 0.001) than other 4 groups;whereas,there was no significant difference among the other 4 groups (5.63-8.05%,0-0%,2.48%-4.85%).(4) Maternal evaluations showed that there was no significant difference of WW,UW,KW% and HW% among 5 groups,but the LW% in G4was significantly higher than other 4 groups (P < 0.05).Conclusion The results of this study indicated that oral administration of aqueous extract of RAM at or below 32 g/kg/day did not cause significant fetal abnormality,external and skeletal malformation in mice;and it did not cause significant cytotoxicity in cultured ESCs;however,32 g/kg/day might cause potential maternal liver toxicity.Our data was meaningful to provide valuable reference for clinical use of herbal medicine in pregnant women.