Objective To observe the expression of angiotensin-converting enzyme( ACE) and ACE2 in rat lung and kidney at different time point after smoke inhalation injury and to explore the possible mechanism. Methods Thirty healthy male SD rats were randomly divided into five groups( n = 6 in each group) , ie. a normal control group, and 4 injury groups of 1 h, 4 h, 10 h and 24 h respectively after 30 min of dense smoke inhalation. The rats were sacrificed at different time point. Lung and kidney tissue samples were collected for measurement of lung wet/dry weight ratio( W/D) , pathological study by HE staining, and ACE and ACE2 expression by immunochemistry staining. Results The inhaled rats all displayed acute lung injury symptoms. The lung W/D in the injury groups were significantly higher compared to the normal control group ( P lt; 0. 05, P lt; 0. 01) . ACE and ACE2 were expressed on cellular membrane of normal lung and kidney. The expression of ACE in lung was increased immediately after injury and the expression of ACE2 in lung was increased at 4 h after injury. No significant changes of the expression of ACE and ACE2 in kidney were observed in the five groups. Conclusion The imbalances of expression of ACE and ACE2 in lung might play an important role in the pathogenesis of smoke inhalation injury.