Mannose-binding lectin (mbl), one of the important components of innate immunity, can activate the lectin pathway of the complement system. After binding mannose containing carbohydrate structures of foreign antigen, mbl initiates and regulates the inflammatory responses. Asthma is a complex inflammatory disease of the lung involving many components of the immune system. Our objective was to investigate the serum mbl levels of asthmatic children in comparison with healthy controls. Serum mbl levels were determined by nephelometric assay in 72 asthmatic children (5–15 yr old) and 30 healthy age-matched controls. Mbl levels of asthmatic children were measured both during acute attack and after complete remission. There was no significant difference between the mbl levels during acute attack (median 4.1 mg/l) or quiescence of symptoms (median 3.6 mg/l). Serum mbl levels both during acute attack or quiescence of symptoms was significantly higher in asthmatic children than in the healthy controls (median 2.8 mg/l, p < 0.0001 for each). Furthermore, mbl levels of asthmatic children positively correlated with peripheral blood eosinophils (r = 0.377, p < 0.001), which is a systemic component of airway inflammation in asthma. Our findings indicate that mbl may be implicated in the pathogenesis of asthma by contributing to airway inflammation or by increasing the risk of developing asthma.