We previously developed a new risk score to predict intravenous immunoglobulin (IVIG) resistance in Kawasaki disease. However, the IVIG dosage used in that study (1 g/kg/d for 2 consecutive days) differs from the single infusion of 2 g/kg recommended in the United States and elsewhere. Our aim was to assess the validity and applicability of our risk score in patients treated with a single infusion. We used a database of 1626 patients with Kawasaki disease given initial IVIG treatment at a dose of 1 g/kg/d for 2 consecutive days (n = 990; IVIG- 1 g/kg × 2) or 2 g/kg/d for 1 day (n = 636; IVIG- 2 g/kg × 1) across 17 hospitals in Japan. Patients received the total IVIG dose within 36 hours in IVIG- 1 g/kg × 2 and 24 hours in IVIG- 2 g/kg × 1. We stratified the patients according to a risk scoring system developed to predict IVIG unresponsiveness, based on scores of ≥5 points. We compared the accuracy of prediction between the 2 groups using receiver operating characteristic analysis. Baseline characteristics and clinical outcomes were similar between both groups. The areas under the receiver operating characteristic curve in IVIG- 2 g/kg × 1 were similar to those of IVIG- 1 g/kg × 2. Using a cut-off risk score of ≥5 points, we could identify IVIG resistance in terms of coronary artery abnormalities within 1 month and coronary artery abnormalities at 1 month with equivalent sensitivity and specificity in both groups. Our risk score can be used to predict IVIG unresponsiveness to a regimen based on a single infusion of 2 g/kg IVIG.