The purpose of this research is to explore the relationships among adolescents' mental health, peer relationships, and self-esteem. Electronic questionnaires made in Google Form, distributed to survey the junior and senior high school students of ten municipal high schools in Taichung City. Five hundred forty-four valid questionnaires were collected, analyzed with SPSS and AMOS 19.0 statistical software. The results showed: Firstly, Adolescents' mental health has a positive influence on peer relationships. Secondly, adolescents' mental health has a positive influence on self-esteem. Thirdly, adolescents' self-esteem has a positive influence on peer relationships. In conclusion, as far as adolescents' mental health, peer relationship, and self-esteem were concerned, adolescents' mental health has the most significant influence on peer relationships in which adolescents' mood status obviously influences mental health.