© 2020, Galenos. All rights reserved.INTRODUCTION: Human paraoxonase-1 (PON1) is one of the endogenous antioxidant molecules working against oxidative stress. We aimed to investigate serum PON1 activity in children with acute bronchiolitis. MATERIALS and METHODS: A total of 29 children aged between 3-21 months with acute bronchiolitis and 35 age-matched healthy controls were included in the study. Bronchiolitis patients were further classified as mild (65%) and moderate (35%). Paraoxonase and arylesterase activities of PON1 were compared between patients with acute bronchiolitis and the control group. RESULTS: Paraoxonase activity of children with acute bronchiolitis was lower than healthy controls but the difference was not significant (127.53 ± 64.17 U/L versus 153.95 ± 74.40 U/L) (p=0.13). Arylesterase activity was significantly decreased in children with mild and moderate bronchiolitis in comparison to the control group (142.43± 56.60 kU/L and 103.70± 26.03 kU/L versus 201.09± 57.26 kU/L) (p<0.001). CONCLUSIONS: Serum PON1 activity was lower in children with acute bronchiolitis compared to controls. Increasing antioxidant capacity may be an effective means of therapy in viral induced lung disease.