Objective To investigate the impacts of cytokines （interleukin-4，IL-4；tumor necrosis factor-α，TNF-α） and medications of bronchial asthma （dexamethasone，aminophylline，salbutamol） on the activity of histamine N-methyltransferase（HMT） in tracheal epithelial cells.Methods BEAS-2B bronchial epithelial cells were cultured and treated with different concentration of TNF-α, IL-4, dexamethasone, salbutamol and aminophylline respectively. The activity of HMT in BEAS-2B cells was determined by high performance liquid chromatography.Results The activity of HMT in tracheal epithelial cells was (50±7) pmol?min-1?mg pro-1.TNF-α and IL-4 lowered the activity of HMT significantly at the concentration equal to or higher than 1 ng/mL and 5 ng/mL respectively，and reached the maximum inhibitory effect at the level of 10 ng/mL.Dexamethasone and aminophylline could ameliorate distinctly the inhibitory effect of TNF-α on the activity of HMT, while salbutamol had no significant inhibitory effect.Conclusions TNF-α and IL-4 exert the lowering effect on the activity of HMT，which would be one important cause of airway hyperreactivity.Glucocorticoids and theophyllines are administered to treat asthma partly due to its relieving mechanism of TNF-α negative effects on HMT.