Backgrounds & aim: Wheezing after bronchiolitis is known as a risk factor for asthma. No cure or effective vaccine has been identified for such disease. The purpose of this study was to determine the effects of zinc sulfate on persistent wheezing after bronchiolitis in infants less than two years. Methods: The present randomized clinical trial study was conducted on 90 infants under two years of age suffering from the first attack with a clinical diagnosis of bronchiolitis wheezing hospitalized in Imam Sajjad Hospital, Yasuj. All infants were equally placed in test groups and control group. In addition to bronchiolitis usual treatment, test group received 20 mg of elemental zinc for seven days. Patient information including risk factors associated with wheezing and persistent wheezing were compared 48 hours and two weeks after treatment. Data were analyzed using chi-square and t tests. Results: In all 90 infants diagnosed with bronchiolitis, wheezing was observed. After 48 hours and two weeks wheezing was continued in 67 patients (74.4%) and 54 patients (60%) respectively Conclusion: The results showed Zinc sulfate had no effect on the improvement of wheezing after bronchiolitis.