Objective To study the efect of montelukast for improving bronchial hyperresponsiveness (BHR) in treatment of bronchiolitis. Methods Four hundreds infants, 3 to 24 months old, hospitalized with acute bronchiolitis in three Hospitals (Urumqi Children’s Hospital, Pediatrics Department of First Ailiated Hospital of Xinjiang Medical University, and Pediatrics Department of Army General Hospital) from January, 2007 to January, 2008, were randomly assigned into four groups: placebo group (n=92), budesonide group (n=91), montelukast short-course group (7 days, n=88), and montelukast long-course group (28 days, n=90). Main outcome measure was BHR ater treatment, including recurrent bronchiolitis wheezing and asthma incidence rate. Secondary measures were changes in serum T-IgE level and eosinophilic cationic protein (ECP) level. Results All four groups were comparable at baseline. No signiicant diferences were observed between placebo group and budesonide group in changes of serum T-IgE (F=6.17, P=0.00), ECP (F=8.13, P=0.00), recurrent post-bronchiolitis-wheezing (χ2=49.46, P=0.00) and asthma incidence rate (χ2=27.21, P=0.00). Ater treatment with montelukast, there was statistical signiicance in T-IgE and ECP level, times of recurrent bronchiolitis wheezing and asthma incidence rate, as follows, montelukast short-course group versus placebo group (F=12.56, P=0.00), montelukast short-course group versus budesonide group (F=7.22, P=0.00), montelukast long-course group versus placebo group (F=20.48, P=0.00), montelukast long-course group versus budesonide group (F=13.56, P=0.00), montelukast short-course group versus montelukast long-course group (F=1.04, P=0.00). Conclusions Budesonide treatment for 7 days can not improve bronchial hyperresponsiveness induced by bronchiolitis, while montelukast does, that is, montelukast can decrease both the times of bronchiolitis wheezing and asthma incidence rate. Long-course treatment of montelukast is superior to that of short-course.