The purpose of this study was to classify the subtypes of aggression in children and adolescents living in foster care to confirm the characteristics of overt aggression and relational aggression. The research sample included a total number of 848 children and adolescents with psychological disorders in foster care. When exploring the differences in the mean of each subtype of aggression, the results varied according to age and gender. As a result of confirming the differences of problem behaviors according to aggressiveness in four groups, the overtly-relationally aggressive groups showed the highest score and all the problem behaviors were serious. In terms of externalizing problems, the overt aggressive groups had more problematic behavior than the general groups. In terms of internalizing problems, the relational aggression groups had higher scores than the general groups.