OBJECTIVE： To observe therapeutic efficacy and safety of budesonide and formoterol in the treatment of acute exacerbation of mild to moderate asthma. METHODS： A total of 89 patients with acute exacerbation of mild to moderate asthma were randomized divded into study group （45 cases） and control group （44 cases）. Study group was given Budesonide and formoterol dry powder inhalation， one inhalation， q6 h， gargling 5 times after inhalation， 6 inhalation per day at most+Montelukast tablet 10 mg orally， once a day. Control group received Prednisone tablet 25 mg orally after breakfast， once a day， d1-5+Theophylline sustained-release capsule 0.2 g， twice a day+Montelukast tablet 10 mg， once a day in the evening. Both groups were treated for 5 d. Acute AQLQ score， FEV1， PEF％pred and SpO2 were observed in 2 groups before and after treatment， and the occurrence of ADR was recorded. RESULTS： Before treatment， there was no statistical significance in acute AQLQ score， FEV1， PEF％pred or SpO2 between 2 groups（P＞0.05）. After treatment， acute AQLQ score， FEV1， PEF％pred and SpO2 of 2 groups were significantly higher than before treatment， with statistical significance （P＜0.05），but there was no statistical significance between 2 groups （P＞0.05）. There was statistical significance in the incidence of ADR between 2 group（P＜0.05）. CONCLUSIONS： Budesonide and formoterol can improve pulmonary ventilation function and prognosis in patients with acute exacerbation of mild to moderate asthma with good safety.