The purpose of this study was to investigate the influence of parent and peer attachment on school adjustment of 5th and 6th graders. In order to achieve this research purpose, following research questions were established. First, does attachment to parents influence on school adjustment of 5th and 6th graders? Second, does attachment to peers influence on school adjustment of 5th and 6th graders? Third, what are relative influences of parent and peer attachment on school adjustment of 5th and 6th graders? Three hundred eighty nine 5th and 6th graders in Busan participated in this study and completed Inventory of Parent and Peer Attachment and School Adjustment Scale. Collected data were analyzed using Two-way ANOVA and ${eta}^2$. The major findings of this study were that parent attachment and peer attachment would significantly influence on school adjustment of 5th and 6th graders; Relative influence of Parent attachment and peer attachment would differ depending upon sub-factors of school adjustment. These results were discussed in terms of theoretical and practical implications. Finally, the limitations of this study were commented and suggestions for future research were made.