Abstract:To investigate the chemical composition characteristics and antimicrobial activities of different rosemary essential oils from different distillation stages，fresh rosemary stems were taken as raw material in this study，and steam distillation was employed to obtain essential oils from seven distinct distillation stages. The components and their relative contents in essential oils from each distillation stage were determined by gas chromatography-mass spectrometry（GC-MS）.Their antimicrobial activities against Escherichia coli and Staphylococcus aureus were evaluated through filter paper method.The findings indicated a significant decrease in essential oil yield as distillation progressed. 52 components were identified among the seven distillation stages，mainly comprised of terpenes，ketones，epoxy compounds，terpenols，phenols，aldehydes，and ester compounds. Of these，36 compounds were common constituents across different distillation periods. The relative contents of trans-sabinene hydrate and 3-hydroxy-β-cyclocitral gradually decreased from 0.09%-0.15% to 0%as the distillation proceeded，while the relative contents of 10 compounds increased from 0% to 0.2%-2.4%.Essential oils from all seven distillation stages exhibited antimicrobial activity against both E. coli and S. aureus. The antimicrobial activity of the essential oils increased gradually as the distillation progressed，with the strongest antimicrobial activity occurring at the seventh distillation stage. In summary，the essential oils obtained from different distillation stages of rosemary demonstrated significant variations in oil yield，chemical composition，and antimicrobial activity.