This study was intended to understand whether emotional regulation program has an effect on decreasing young child's aggression, performing the program to children, who showed aggression by the flaw of emotional regulation, for the study. The participants were 6 children, who displayed more than 70T in aggression scale in Korean Child Behavior Checklist (K-CBCL) and belonged to the bottom 25% in an emotional regulation test, and they were equally divided into an experimental group and a control group. The study addressed the following questions. First, did the program have an effect on the decrease in young child's aggression? Second, did the program have an influence on the decrease in young child's aggression during the program? Third, was an effect on the decrease in young child's aggression found in the general scene? The results of this study were as follows: First, emotional regulation program decreased parents-reported and teacher-reported aggression (interpersonal relationship, externalized aggression). emotional regulation program reduced young children's aggressive behaviors (a substitute, a person, linguistic aggression). Second, young child's aggressive behaviors (a substitute, a person, linguistic aggression) in the general scene fell by emotional regulation program. Even though there is a limitation due to a case study design, emotional regulation program proved its effects on decreasing young children's aggression.