Objective To observe the effect of Shoutai Pills on endometrial decidualization of mice with recurrent spontaneous abortion(RSA);To explore its possible mechanism in the treatment of RSA based on histone modification.Methods Totally 40 female CBA/J mice were divided into normal group,model group,Shoutai Pills low-dosage group(7.5 g/kg),Shoutai Pills high-dosage group(15 g/kg)and dydrogesterone group(3 mg/kg).The normal group were co housed with BALB/C male mice,while the other groups were co housed with DBA/2 male mice to establish an RSA mouse model.After modeling,the administration groups were given corresponding medication solution by gavage,while the normal group and model group were given equal volume of pure water by gavage for 10 consecutive days.The embryo condition was observed and the embryo loss rate was calculated,ELISA was used to detect serum prolactin(PRL)content,HE staining was used to observe the morphological changes of decidual tissue,RT-PCR was used to detect PRL mRNA expression in decidual tissue,Western blot was used to detect the protein expressions of H4ac,H3K27ac,H3K27me3.Results Compared with the normal group,the model group mice showed a significant increase in embryo loss rate,a significant decrease in serum PRL content,disordered arrangement of decidual cells,and extensive bleeding and necrosis;the expression of PRL mRNA and protein in decidual tissue significantly decreased,the protein expressions of H4ac and H3K27ac significantly decreased,while the expression of H3K27me3 protein significantly increased,with statistical significance(P<0.05).Compared with the model group,the embryo loss rate of Shoutai Pills low-and high-dosage groups and the dexamethasone group significantly decreased,the serum PRL content significantly increased,tightly arranged decidual cells,reduced necrosis,and intact glands;the expression of PRL mRNA and protein in decidual tissue of mice in Shoutai Pills high-dosage group and the dexamethasone group significantly increased,the protein expressions of H4ac and H3K27ac significantly increased,the expression of H3K27me3 protein significantly decreased,with statistical significance(P<0.05).Conclusion Shoutai Pills can promote endometrial decidualization in RSA mice,which is related to the changes of histone modification in endometrial stromal cells.