In this study, we investigated whether ambroxol significantly affects secretion, production and gene expression of mucin from cultured airway epithelial cells. Confluent primary rat tracheal surface epithelial (RTSE) cells were pretreated with adenosine triphosphate (ATP) for 5 min and then treated for 30 min with ambroxol to assess the effect on mucin secretion using ELISA. Additionally, confluent NCI-H292 cells were pretreated with ambroxol for 30 min and then stimulated with EGF or PMA for 24 h. The MUC5AC mucin gene expression and mucin protein production were measured by RT-PCR and ELISA. The results were as follows: (1) ambroxol did not significantly affect ATP-induced mucin secretion from cultured RTSE cells; (2) ambroxol inhibited the production of MUC5AC mucin protein induced by EGF and PMA in NCI-H292 cells; (3) ambroxol also inhibited the expression of MUC5AC mucin gene induced by EGF and PMA in NCI-H292 cells. This result suggests that ambroxol can inhibit the production and gene expression of MUC5AC mucin, by directly acting on human airway epithelial cells.