Inconsistent results have been reported on the effects of distraction on negative emotions during medical procedures in infants. These differing results may be attributable to the fact that the effects are apparent under a mildly stressful medical procedure. A total of 17 infants, 18 preschoolers, and 15 school-aged children who were hospitalized were administered, monitoring for vital signs, a mildly stressful medical procedure, by a nurse in a uniform with attractive character designs as a distractor. Consistent with the hypothesis, participating infants showed fewer negative behaviors and lower salivary α-amylase levels when distracted. The results support the efficacy of distraction in infants under a mildly stressful medical procedure.