OBJECTIVE: To study the effect of dexamethasone(DXM) on the cellular DNA synthesis and airway remodelling of airway in asthmatic rats. METHODS: Asthmatic model was established using SD rats. The changes of the airway wall were observed by coll agen and mucus staining and Bromodeoxyuridine(Brdu)-positive cells were detecte d using immunohistochemical technique in the airway smooth muscle(ASM) and epit heli um in the asthmatic model rats(model group), DXM inhalation rats(DXM group), a nd normal rats(control group). RESULTS: ① The collagen d eposition in the subepithelium and mucus staining in the airway obviously decreased in the DXM group compared with the model group.②The Brdu-positive cells of ASM in the model group(10.25±2.09) were significantly higher than those in the control group(7.15±2.05) and the DXM group(6.85±2.20)(P<0.01). The Brdu-positive cells of the epithelium in the model group(21.83±7.01) were also significantly higher than those in the control group(16.22±4.36) and the DXM group(16.92±3.48)(P<0. 05). CONCLUSIONS: Inhaling DXM may alleviate airway inflammation response, inhib it DNA synthesis of airway cells and prevent from developing airway remodelling in asthmatic rats.