The purpose of this study is to identify the influences of parental attitude, parenting attitudes, family function and peer attachment on the self-efficacy of middle school students in multicultural families. In particular, peer attachment was used as a mediator to determine the effects of self-efficacy. 302 multicultural family adolescents who enrolled in Seoul and Gyeonggi-do middle schools were surveyed. In order to measure the variables, this study used such scales as parenting attitude scale, family function scale, peer attachment scale and self efficacy scale. The results were analyzed by the PASW 18.0 program. The findings of the study led to the following conclusions; First, it has shown that peer attachment was the only variable that had significant differences by sex in middle school students of multicultural families. Second, the most influential variables of self-efficacy of middle school students in multicultural families was peer attachment among parenting attitude, family function and peer attachment. Third, there was a mediating effect of peer attachment among parenting attitude, family function and self-efficacy for adolescents of multicultural families. The notable distinction of this study was to find that peer attachment variable is the most important factor of self-efficacy. Considering the results in this study, aggressive intervention is necessary in order to improve the self-efficacy of middle school students in multicultural families.