The present study is a single blind, randomized clinical trial with placebo control that evaluates the effect of low-dose ketamine in treating asthmatic patients presented to the emergency department. Patients with mild to moderate asthma, aged between 18 to 85 years old,and without any prohibition for using IV ketamine were entered. If the patient’s clinical condition worsened during the study, or needed ventilator support for respiration or showed ketamine side effects, would be excluded. Patient's divided in 2 group and each group contained 46 patient. Both groups received basic treatments of asthma attack with standard doses including inhaled beta agonists and anticholinergics, and IV corticosteroids. The intervention group received IV ketamine with 0.3, 0.4, or 0.5 mg/kg doses in addition to the standard treatment. Peak expiratory flow rate (PEFR) was measured and recorded before and 30 minutes after treatment for all patients. At the study beginning, the peak expiratory flow for each patient was measured and then compared to their expected natural flow based on their sex, age, and height, and if it was lower than 70% of the normal rate, the case was considered as acute asthma attack. After 30 minutes we will check the peak expiratory flow again and if PEFR will greater than 70% the treatment approach achieved.