The relationships between attachment to parents, attachment to friends, and adolescent delinquency have been issues that many researchers have paid attention. However, Most of them have been analyzed with cross-section data so far. This means that independent variables did not precedes dependent variables. Therefore, this study examined the relationships between parents attachment, friends attachment, and adolescent delinquency with longitudinal design. Data were selected from 2003(wave 1)-2004(wave 2) KYPS. Participants were 3449 middle school students(1725 boys, 1724 girls). Hierarchical regression revealed that: (1) attachment to parents negatively influenced adolescent delinquency, while attachment to friends positively influenced their delinquency. (2) a mild moderating effect of parents attachment: only when parents attachment is low, friends attachment positively influenced after a year adolescent delinquency. This result suggest that friends are more significant among adolescents who are not sufficiently served attachment from their parents.