Ethnopharmacological relevance: Xiaoyaosan (XYS), a classical Chinese prescription, has been clinically employed to treat depression in recent years.In our previous experiments, XYS was divided into several different polar fractions and animal experiment was conducted to evaluate the antidepressant effect of each fraction.Consequently, XY-A fraction was preliminarily confirmed to be the most effective part, followed by XY-B fraction.Aim of the study: This study was design to re-verify the anti-depressant effect of the two effective fractions on the basis of behavior research and metabonomics.Meanwhile, we aim to explore whether the mixture of the two fractions with an equal proportion is prior to the single fraction and to investigate which dose is superior among compatibility groups.Materials and methods: A mouse model of depression was established through chronic unpredictable mild stress (CUMS).The rats were randomly assigned to 8 groups and orally administered with two effective fraction alone as well as their compatibility at different doses during the 21 days model building period.At different predetermined time points, behavior tests were conducted.Metabolic profiling of the plasma was performed by using gas chromatography coupled with mass spectrometry.Acquired data were subjected to PLS-DA for differentiating the model group, the control group and the administration groups.Potential biomarkers were screened by using multivariate statistical analysis to evaluate the regulatory ability of each administration group.Result: Based on behavior and metabonomics results, we further prove that the two fractions are the active fraction of XYS and that XY-A is superior to XY-B.Among compatibility groups, XY-A2B2(the middle dose group) demonstrated the best anti-depressant efficacy, and it is prior to XYS original prescription.No significant difference between XY-A group and XY-A2B2 group was observed from PLS-DA score plots.However, among 13 metabolites identified in plasma, the level of 10 metabolites were significantly regulated in XY-A2B2 group while XY-A group could only regulate 4 metabolites, indicating that compatibility group of the two effective fractions at middle dose demonstrated better anti-depressant efficacy.It was suggested that metabonomic profiling based on GC/MS is a more sensitive method than behavioral approach.