Objective To explore the possible mechanism of Jianwei Shoutai Pill（减味寿胎丸） for treating spontaneous abortion. Methods Female mice were divided into healthy pregnancy group

spontaneous abortion model group

dydrogesterone group

and Jianwei Shoutai Pill group

with six mice in each group. Female CBA/J mice were mated with male BALB/C mice in normal pregnancy group

while in other groups the mating of CBA/J females and DBA/2 males was used to establish the spontaneous abortion model. The mice were bred at a female to male ratio of 1 ∶1. The vaginal plug of female mice was checked next morning to see if there was sperm on vaginal plug or the smear

which would be designated as day 0 of pregnancy. From day 0 to day 9

mice in normal pregnancy group and spontaneous abortion model group were administered with 0.01 ml/g pure water by gavage

while mice in Jianwei Shoutai Pill group and dydrogesterone group were given 2.72 g/（kg·d） Jianwei Shoutai Pill and 12.3 mg/（kg·d） dydrogesterone by gavage respectively. After nine days

changes in the mice body weight

the number of congestion or absorbed embryos

and the embryo diameter were measured. Hematoxylin and Eosin（HE） staining was used to assess the morphological changes of decidua. Immunohistochemical staining was used to measure the positive expression of forkhead box transcription factor 3（FOXO3）. Western blot was used to detect the protein expression of FOXO3 and progesterone receptor（PR） in decidua. Results There were no significant differences between groups in mice body weight and embryo diameter（P>0.05）. The abortion rate of abortion model group was 60.98%

significantly higher than that of normal pregnancy group（8.89%）

Jianwei Shoutai Pill group（23.40%） and dydrogesterone group（22.92%

P<0.017）. HE staining result showed that the decidua columnar epithelium covered all the surface of the uterine cavity

and the decidua glands were abundantly distributed in the normal pregnancy group. In the abortion model group

the uterine cavity contained significant amounts of blood cells

the decidua was shed off

and the decidua layer became thin. Compared to the abortion model group

there were less reduced glands and more regular structure of the decidua in Jianwei Shoutai Pill group and dydrogesterone group. The decidua FOXO3 and PR protein expression significantly reduced in abortion model group than in normal pregnancy group（P<0.05）; those of Jianwei Shoutai Pill group and dydrogesterone group significantly increased when compared to abortion model group（P<0.05）; and there was no statistically significant difference between Jianwei Shoutai Pill group and dydrogesterone group（P>0.05）. Conclusion Jianwei Shoutai Pill may reduce mice abortion rate by up-regulating FOXO3 and PR protein expression in decidua.