Objective: To study on the mechanism of Siwutang in treating primary dysmenorrhea syndrome from the aspect of endogenous metabolites. Method: Dysmenorrhea rat model was constructed by injecting estradiol benzoate and oxytocin.UPLC-Q-TOF-MS was employed to analyze fingerprint of metabolites in plasma of dysmenorrhea rats under electrospray ionization positive and negative ion mode

the acquired metabolites were identified by mass spectrum informations and public database retrieval.Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were adopted to screen the differential metabolites among the normal group

dysmenorrhea model group and Siwutang group;these different metabolites among three groups were analyzed by KEGG metabolic pathway method. Result: Twenty-three endogenous metabolites from dysmenorrhea model rats were detected and identified;when the dysmenorrhea model group compared with the normal group

progesterone

cortexolone

tauroursodeoxycholic acid and lysophosphatidic acid were the different metabolites with variable importance in the projection (VIP)>1 and P<0.05.When the Siwutang group compared with the model group

L-phenylalanine

L-tyrosine

N-benzoylglycine

L-methionine

cortexolone and stearic acid glycinamide were the different metabolites with VIP>1 and P<0.05. Conclusion: Siwutang has a certain callback effect on the differential metabolites in primary dysmenorrhea rats

its therapeutic mechanism is mainly related to steroid synthesis

lysophosphatidic acid metabolism and amino acid metabolism.