Abstract: OBJECTIVE The experiment was designed to investigate the changes of the chemical constituents from the essential oils of Baizhu Shaoyao San and the medicinal herbs contained in Baizhu Shaoyao San. METHODS The essential oils from Baizhu Shaoyao San and the medicinal herbs (stir-baked Atractylodis Macrocephalae Rhizoma， stir-baked Paeoniae Radix Alba， stir-baked Citri Reticulatae Pericarpium， Saposhnikoviae Radix) contained in Baizhu Shaoyao San were extracted by steam distillation method. GC-MS combined with automated mass spectral deconrolution and identification system (AMDIS) and retention index were employed to identify the chemical components of the essential oils and the relative amounts of these chemical constituents were calculated by peak area normalization method. RESULTS The results showed that the essential oils of Baizhu Shaoyao San were mainly derived from stir-baked Atractylodis Macrocephalae Rhizoma， stir-baked Citri Reticulatae Pericarpium， and Saposhnikoviae Radix. The quantity and quality of the volatile constituents from the medicinal herbs contained in Baizhu Shaoyao San experienced apparent changes after their compatibility. CONCLUSION Our investigation can make a good foundation for the material basis and the compatibility mechanism of Baizhu Shaoyao San.