Kawasaki disease (KD) is an acute febrile disease of unknown etiology that develops in children and is sometimes accompanied by myocardial dysfunction and systemic vasculitis. However, myocardial repolarization lability has not yet been fully investigated. Thus, the objective of this study was to evaluate myocardial repolarization lability (QT variability index-QTVI) based on the body surface electrocardiograms in the acute and recovery phases. The subjects were 25 children with acute KD who were hospitalized for treatment. An equal number of age-matched healthy children were selected as controls. The RR-intervals and QT-intervals were measured based on a body surface electrocardiogram of 120 consecutive heartbeats to calculate the QTVI. The QTVI values were then compared with the acute and recovery phases. The relationships between blood biochemistry data and QTVI values were also examined. QTVI was significantly decreased from the acute phase to the recovery phase (P < 0.05) and then recovered to the same level as that of the control. QTVI in the acute phase showed a significant positive relationship with body temperature and C-reactive protein (P <0.05). QTVI was high in the acute phase and was correlated with an inflammatory reaction and became normalized during the recovery phase.