Introduction: Asthma is one of acute respiratory diseases leading to emergency department (ED) referral. Management of acute attack plays an important role in its outcome. Objective: This trial was designed to evaluate the effectiveness of nebulized budesonide versus placebo in moderate to severe acute asthma attack in adults in the ED. Method: In this clinical trial, we enrolled patients with acute exacerbation of asthma and standard treatment of acute asthma attack was administered to all of them. 41 patients in our study were randomly entered into 2 groups. In one group, we prescribed nebulized budesonide and in the other group nebulized placebo (normal saline) was administered. Patients’ demographic data, vital signs, symptoms’ acuity and the time of symptom relief, patient and physician satisfaction were all recorded and compared between the 2 groups. All cases were followed and disease outcome, readmission, mortality and morbidity rates were documented. Results: In this study, 20 patients were entered the budesonide group and 19 patients were enrolled in the placebo group. The mean age ranges were 55. 70± 15. 30 and 60. 32± 18. 41 years old respectively. Heart rate, respiratory rate and O2 saturation in the first group were improved significantly after the treatment in comparison to the second group (p<0. 05). The mean time of recovery and length of hospital stay were better in the first group than the second group but this difference was not significant (p>0. 05). Conclusion: The addition of nebulized budesonide to standard asthma treatment might result in more improvement in O2 saturation and less patient’ s distress.