Kawasaki disease (KD) is the leading cause of systemic vasculitis syndrome in infants and in young children, although its cause has still not been elucidated. Coronary aneurysm (CA) is a major and important complication of KD. Patients resistant to intravenous immunoglobulin (IVIG) treatment are at a high risk of CA. Infliximab (IFX) is a chimeric monoclonal antibody that specifically binds to tumor necrosis factor-alpha (TNF-α) and has been successfully used in some cases of IVIG-refractory KD. However, optimal timing for the administration of IFX has not yet been determined. We present a case of a 2-year-old boy with IVIG-refractory KD who developed a giant right coronary artery (RCA) aneurysm after successful treatment with IFX. Treatment with IVIG (2 g/kg), prednisolone (PSL, 2 mg/kg/day), and aspirin (50 mg/kg/day) was initiated on day 2 because of the fulfillment of KD criteria. Additional IVIG (2 g/kg) and ulinastatin (20,000 U/kg) treatment on day 5 and intravenous administration of IFX (5 mg/kg) on day 9 effectively lowered the patient's fever and improved laboratory data. However, the RCA continued to balloon into a giant CA, from 7.3 mm on day 9 to 14.3 mm in diameter at 2 months. IFX is one treatment option for IVIG-refractory KD. However, the timing and indication of IFX treatment should be carefully determined.