Purpose: Collectin family is an important component of innate immunity, of which surfactant protein (SP)-D and mannose-binding lectin (MBL) are the most characterized. We examined SP-D and MBL in young children with acute respiratory syncytial virus (RSV) bronchiolitis. Methods: Sixty-three children (≤24 months of age) admitted with the first RSV bronchiolitis during 2 epidemics and followed for 1 year after discharge were enrolled. The patients were defined as severe group when they had 2 of followings during admission: hypoxemia (<92% oxygen saturation), rapid breathing (and/or lower chest wall indrawing), and >7 days of hospital stay. All children were evaluated if they had recurrent wheezing during follow-up. SP-D and MBL were measured using enzyme-linked immunosorbent assay in serum collected on admission and compared with controls. Their levels were evaluated in relation to the symptom severity during admission and recurrence of wheezing after discharge. Results: Serum SP-D increased significantly in the patients (P<0.01), but MBL showed no difference compared to the controls. SP-D levels were significantly higher in severe group compared with nonsevere group (P<0.05). SP-D levels in the patients with recurrent wheezing after discharge were significantly higher than in those without (P<0.05). MBL showed no difference in relation to the symptom severity or recurrence of wheezing. Conclusion: Our study showed that serum SP-D was associated with the severity of RSV bronchiolitis and suggests that it might be a biomarker of lung injury and recurrence of wheezing illnesses in the young children admitted with their first RSV bronchiolitis. (Allergy Asthma Respir Dis 2013;1:235-240)