Objective: Coronary artery aneurysm and ectasia are the most important complications of Kawasaki disease(KD). Iron deficiency anemia (IDA) is one of the most prevalent micronutrient deficiencies in the world. Children with IDA are prone to infection and inflammation. We investigate the relationship between coronary artery lesion and iron deficiency anemia as comorbidity in KD. Method: We retrospectively studied 167 patients who were diagnosed as Kawasaki disease in Gangnam Severance Children\'s Hospital from May 2015 to June 2016. Study subjects were assessed for potential coronary artery lesion using two different classifications: presence of aneurysm and severity of ectasia. First, the patients were divided into either the absence (Group 1) or presence (Group 2) of coronary aneurysm group, with the internal diameter of 4mm or greater serving as the definition of aneurysm. Enrolled patients were also classified into three different ectasia groups according to the z-score using BSA. Patients with z-score of 2.0 or below belonged to the absence group (Group 3), while those between 2.0 to 2.5 belonged to the borderline group (Group 4), and those with 2.5 or above to the presence group (Group 5). We analyzed the clinical characteristics and laboratory data of different groups. Results: All the patients’ mean age was 30 months, with the male: female ratio 6:4. In reference to the Kobayashi score, Group 2 showed significantly lower platelet count (p=0.017) and higher neutrophil count (p0.001) than Group 1. Group 2 tended to have higher CRP and lower sodium level. Group 2 participants had lower serum iron level and iron saturation than Group 1, with the difference in serum iron level being statistically significant (p=0.005). There was a decreasing tendency of serum iron level and iron saturation from Group 3 to Group 5, with the iron saturation difference statistically significant (p=0.001). Conclusion: Coronary artery aneurysm, as well as severity of ectasia, showed close correlation with iron deficiency. IDA seemed to be closely associated with coronary artery lesion in Kawasaki patients. Iron deficiency might be a risk factor or comorbidity of KD, affecting its disease course.