This study is aimed to explore the inhibitory effect of essential oil from Chimonanthus zhejiangensis on mast cell activation in rheumatoid arthritis and the efficacy of its main monomer.The essential oil was extracted by hydrodistillation,and gas chromatography-mass spectrometry (GC-MS) was used to analyze the volatile chemical compositions and determine the content of the main component.The cell toxicity of essential oil and the main component was tested by cell counting kit 8 (CCK-8).LAD2 was stimulated by C48/80.The degranulation and release of cytokines from LAD2 at different concentrations of essential oil and its main component were detected by linked immunosorbent assay (ELISA).The positive drug methotrexate was selected as the control.The results showed that the main component of essential oil from C. zhejiangensis was eucalyptol,and its content was 0.805 g/mL;essential oil and eucalyptol could inhibit mast cell degranulation at low,medium and high concentrations,and significantly reduced the release of cytokines including IL-4,IL-8,TNF-α and VEGF;the inhibitory effect of essential oil was better than that of eucalyptol at the same concentration,which was close to the effect of the positive drug.In a conclusion,both the essential oil from C. zhejiangensis and eucalyptol can inhibit the degranulation and inflammatory reaction of mast cells.It can be inferred that the essential oil from C. zhejiangensis has the effect on relieving rheumatoid arthritis,in which eucalyptol plays an important role as the main component.