OBJECTIVE: CD40 and CD40 ligand (CD40L) are a pair of co-stimulatory molecules in immunoreaction, and might play an important role in the development of asthma. This study aimed to explore the relationship between the expression of CD40 and CD40L and the development of asthma in children. METHODS: Thirty-two children with acute asthma were selected randomly and 20 age-matched healthy children were enrolled as controls. Flow cytometry was used to detect the expression of CD40 and CD40L in T and B lymphocytes in peripheral blood. RESULTS: The expression level of CD40 in B cells of asthmatic patients was significantly higher than that of controls (17.05±4.88 vs 13.89±3.67, P < 0.05). CD4~+T cells of asthmatic patients expressed a higher level of CD40L compared with controls (8.04±3.53 vs 5.58±3.00,P <0.05) . CONCLUSIONS: Expression of CD40 and CD40L were increased in relevant immune cells of children with acute asthma, which may contribute to the immune pathogenesis of asthma.