Kawasaki disease (KD) is an acute febrile vasculitic syndrome of unknown etiology that preferentially affects the coronary artery. Interleukin-10 (IL-10) is a key proinflammatory cytokine, and a polymorphism near the major transcriptional start site of the IL-10 gene was shown to influence IL-10 production in vitro. This study investigated the association of the IL-10 promoter polymorphism with KD and its clinical parameters in Korean children. A total of 194 children with congenital heart disease (CHD) and 95 children with KD were included in this study. IL-10 (-627 A/C) polymorphism genotypes were determined using the single-base extension method. There was no difference in the allele frequencies of IL-10 (-627 A/C) polymorphism between CHD children and KD children. KD children with one or two copies of the IL-10 (-627C) allele showed significantly lower albumin levels (p = 0.020) and higher frequencies of early coronary artery aneurysm [62.22% versus 37.78%, adjusted odds ratio (aOR) = 3.50, 95% confidence interval (CI): 1.50-8.16] compared with KD children with the common IL-10 (-627A) allele. These findings suggest that the IL-10 (-627 A/C) promoter polymorphism might be a genetic marker for the risk of early coronary artery complication in KD.