The main purpose of this study was to examine whether different cultures affect attachment style by comparing Korean and American adolescents, with a focus on parent attachment and peer attachment. Data were collected from middle and high school students(291 Korean adolescents, 158 American adolescents), and the participants were asked to report on the revised version of the Inventory of Parent and Peer Attachment(IPPA-R). The analysis showed significant differences on both parent and peer attachment between Korean and American adolescents: Korean adolescents had more negative relationships with their parents compared to American adolescents. In contrast, Korean adolescents had more positive relations(high trust and communication score, low alienation score) with their friends than American adolescents. More results on the relationships between attachment style and socio-environmental variables were presented, and each of these results could be interpreted by cultural difference. Based on these results, parent-child programs and peer programs that can enrich the relationships that a child has with his or her parents and friends were introduced for researchers, educators, teachers, and counselors. The implications and recommendations for future research were also presented.