To explore the relationship between IL-3 gene polymorphism and the levels of serum IL-3 and eosinophil cation protein (ECP) for understanding the role of IL-3 gene polymorphism in the mechanism of childhood asthma.The method of restriction fragment length polymorphism (RFLP) was adopted in detecting +1923 site polymorphism of IL-13 gene in intron 3 region, ELISA was employed in detecting the level of serum IL-13, and fluorescent enzyme-linked immunoassay was used to detect the level of serum ECP.The frequency distribution of TT, TC genotypes of IL-13 Intron 3+1923 site in asthmatic children was higher than that of CC genotype in normal control (P<0.05), and the levels of serum IL-13 and ECP of TT, TC genotypes were significantly higher than those of CC genotype respectively (P<0.01).The close relationship of IL-3 gene polymorphism with the levels of serum IL-13 and ECP suggests that IL-3 gene polymorphism may play an important role in the mechanism of childhood asthma.